Introduction to ArcInfo (Workstation)

Getting started with ArcInfo Getting started with ArcInfo  ArcInfo® is a powerful GIS software technology that enables you to access, integrate, visualize, analyze, and output a world of information. ArcInfo offers a complete solution for the automation, management, and display of geographic and associated data, which can be used by any organization that works with spatial data. With ArcInfo, you can perform a broad range of functions. The software includes tools for creating professional maps, tools for maintaining databases, and a highly sophisticated suite of geographic analysis tools. ArcInfo enables you to integrate vector (x,y locations) map data, raster images such as photographs, scanned documents or satellite images, computer aided drafting (CAD) drawings, sound and video data, as well as a wealth of tabular DBMS data, into a single, integrated environment. ArcInfo software is available for several UNIX® workstations and the Intel NT and DEC Alpha NT platforms.

ArcInfo subsystems ArcInfo subsystems  ArcInfo is made up of several subsystems, each handling a different group of functions. Listed below are the different ArcInfo subsystems written by ESRI®. ARC is the overall GIS manager; it is not a graphic module. You can use ARC to generate and manage coverages in the database, convert data from other digital formats, manipulate spatial and attribute data in one or more coverages, and create new data relationships between coverages. ArcTools™ is a collection of ARC Macro Language™ (AML™) -based tools, implemented through an easy-to-use graphical user interface, for common ArcInfo operations and functions. TABLES™ software is a tabular management system that uses INFO files to create, store, edit, and query tabular data. ArcInfo LIBRARIAN™ software is a geographic data management system which provides tools to create and manage map libraries. ARCPLOT™ is a graphic module for map display and query. You can use it to display and query spatial and attribute data for one or more coverages. You can also use ARCPLOT to create screen displays and maps and generate plot files. ARCEDIT™ is an interactive graphics editor. Use it to digitize and edit one coverage at a time and correct errors in spatial and attribute data. ARC Macro Language (AML) provides full programming capabilities and a set of tools to tailor your application’s user interface. Open Development Environment (ODE) allows you to use standard development environments (e.g., Visual Basic, Visual C++, Delphi, Power Builder, C, Motif, Tcl/Tk) to create applications incorporating ArcInfo functionality. ESRI provides several software extensions that let you expand ArcInfo's capabilities even further. ArcSDE — a special release of ESRI’s Spatial Database Engine™ (SDE™), including SDE for coverages and SDE for the DBMS of your choice. ARC COGO™—for applications requiring accurate coordinate geometry ARC NETWORK™—for linear modeling ARC TIN™—for surface modeling ARC GRID™—for applications requiring raster-based grid-cell analyses ArcScan™—for scan digitizing ArcStorm™—for feature-oriented, geo-relational database management ArcExpress™—for accelerating display performance ArcPress™—for graphics metafile rasterization

ArcInfo data types Vector Raster Supported formats Coverage Map Library ArcStorm Library TIN Shapefile SDE Layer DXF File Grid Image ArcInfo data types  The strength of any GIS lies in the methods available to represent geographic information. ArcInfo supports many data types for representing geographic information. The features it depicts, its method for representing shape and location, and its utility for various geographic operations characterize every geographic dataset. Each model has its own advantages and limitations and supports operations that other data types may not. ArcInfo-supported geographic datasets include the coverage and DXF formats for vector data, grids and images for raster data, and triangulated irregular networks (TINs) and lattices (a grid format) for surface representation. ArcInfo allows you to combine these geographic datasets into a single geographic database. ArcStorm and map libraries organize coverages and INFO files into a logical, manageable framework. ArcInfo also has a variety of tools you can use to convert from non-native formats to an ArcInfo native format. ArcInfo supports conversions for nearly all drawing, GIS, and raster formats produced by other software programs or provided by data vendors.

The coverage Basic unit for vector data Can be point, line, polygon Or region The coverage  A coverage is ArcInfo’s basic unit of storage for vector data. It represents a separate classification, or theme, of data for a geographic area and contains both feature location data and feature descriptive data. Usually, a coverage represents a single map sheet layer in digital form and contains one type of map feature, such as soils, roads, wells, parcels, rivers, or vegetation. In the computer, a coverage is stored as a directory (folder) containing related files describing the locations and attributes of the features contained within it.

Linking features and attributes Because every feature has a unique identifier, the uniqueness of each feature is guaranteed even if it shares attributes or spatial coordinates with another feature. Linking features and attributes  The power of the coverage data model is its ability to link spatial data (both locational and topologic) and attribute data. Locational data tells where features are; topologic data tells where features are in relation to one another; attribute data tells what the features are. Each individual feature contained in a coverage is assigned a unique numerical identifier and is characterized by a unique location (spatial data) and set of attributes (descriptive data). The identifier, a unique number for each feature in the coverage, is stored in both the spatial file and the attribute file. This ensures a strict one-to-one correspondence between spatial and attribute data. The identifier is the key to integrating spatial data with attribute data.

The workspace A directory (folder) Used in an ArcInfo session Contains geo datasets and an INFO The workspace  A workspace directory (folder) is the work area on your computer used during an ArcInfo session. It provides the structure for organizing your work. Workspaces contain geographic datasets, such as coverages, grids, TINs, images, and a local INFO database. The collection of geographic datasets contained in a workspace is stored as a set of subdirectories and files. Coverages, grids, and TINs are stored as directories; images are stored as files. Workspaces can also contain a number of other ArcInfo data files, such as macros and menu files written in AML, key legend files, and maps in the form of ArcInfo graphics files. In addition to the geographic datasets, ArcInfo workspaces contain an INFO database stored in a workspace subdirectory named INFO. The INFO database stores and manages feature attribute tables and related tables for all the geographic datasets in the workspace. Any directory that contains an INFO subdirectory will be recognized by ArcInfo as a workspace. You can create a workspace at any level where you have write access. Although a workspace can contain no, one, or many coverages, it can contain only one INFO directory.

Workspace commands COPYWORKSPACE CREATEWORKSPACE DELETEWORKSPACE LISTWORKSPACE RENAMEWORKSPACE WORKSPACE (or &WORKSPACE) Use the ARC commands listed below or the ArcTools interface to create and manipulate workspaces. COPYWORKSPACE—copies the contents under one workspace to another CREATEWORKSPACE—creates a workspace DELETEWORKSPACE—deletes all files and directories contained in the specified workspace LISTWORKSPACE—lists the ArcInfo workspaces located under the given or current directory RENAMEWORKSPACE—renames a workspace WORKSPACE (or &WORKSPACE)—lists your current workspace directory location or moves you to a specified workspace directory Because your operating system does not know and cannot maintain the relationships of ArcInfo datasets to the INFO database, do not use operating system commands to copy, move, delete, or rename ArcInfo datasets.

The geographic database Core of a GIS Completeness Accuracy Spatial data Attribute data The geographic database  A geographic database is the foundation of every GIS. Its completeness and accuracy affect all the applications it supports. It is a collection of data for features located within the same real-world space and is organized in such a way as to efficiently serve one or more applications. A geographic database should be maintained by a set of well-documented and well-administered procedures. A unique identifier links the two components of geographic data: spatial data and attribute data. To be efficient, different types of data are stored as different structures. Attribute data is stored in tables and managed by a relational database management system (RDBMS). Spatial data is stored in files and managed by the GIS software. Geographic features are organized into layers, or themes, of information. For example, a basemap can be organized into themes, such as administrative boundaries, streams, water bodies, roads, contours, and control points. Features may be organized by what they represent (streams and roads are both line features, but may be stored in separate layers because their attributes differ). Point, line, and polygon features may be stored as separate layers.

Operating ArcInfo Arctools (buttons+menus) Command-driven interface Limited to functions included Command-driven interface Customized/automated by AML Open Development Environment (ODE) Visual Basics, C, C++, Delphi, Power Builder Operating ArcInfo  You can operate ArcInfo in several modes. You can enter commands at the program prompt, run AML programs that may contain ArcInfo commands, and use the ArcTools menu-driven interface to perform common ArcInfo operations. You can issue ArcInfo commands at the program prompt to perform a specific task. Each command has one or more arguments that may require user input. Groups of ArcInfo commands can be combined with AML directives, functions, and variables to perform a series of ArcInfo tasks. You may be prompted for input while the program is running. ArcTools provides an easy-to-use menu interface for common ArcInfo operations. Rather than entering commands, you select menu choices that run ArcInfo programs in the background. An important adjunct to using ArcInfo in any mode is the online Help system that contains documentation for ArcInfo commands and concepts. The Open Development Environment (ODE) provides a method for using standard developer tools to create applications that incorporate ArcInfo functionality. When using ODE, you are still sending commands to ArcInfo, but rather than using AML macros, you can use the development environment of your choice. To use ODE effectively, you will still need to be familiar with ArcInfo commands and AML elements (directives, functions, and variables). Some of the development environments you can use are: UNIX—C, Motif, Tcl/Tk; Windows NT—Visual Basic, Visual C++, Delphi, and Power Builder.

ArcInfo Commands Syntax rules <cover> <> Required argument {} optional argument {COVER} Uppercase indicates a KEYWORD Lowercase substitute the name of an object <POINT|LINE|POLY> Choices are separated by vertical bars {POLY|LINE|POINT} For optional argument, first choice is the default # Optional argument place holder * Indicates the input for argument comes from the cursor ArcInfo commands  ArcInfo commands execute programs that perform GIS operations. Command syntax is defined by the name of a command combined with its required and optional arguments. By observing syntax conventions, you can interpret which information you must provide to obtain the desired result. Separate the command name from subsequent arguments by at least one space. Always start the command line with the command name. If a command fails due to a missing argument, you must reissue the entire command line. Use the # symbol as a place holder when you skip optional arguments, allowing the system to substitute a default value. Example command line: Arc: USAGE CLEAN Usage: CLEAN <in_cover> {out_cover} {dangle_length} {fuzzy_tolerance} {POLY | LINE} Arc: CLEAN STREET STREET2 # # LINE You can use the mouse or cursor to pick or locate a feature on the screen using the * symbol. You will use this technique more often than its alternative that specifies location with explicit coordinates (i.e., {* | x y}). Required arguments demand that you select a keyword from the available choices; however, optional arguments default to the first keyword in the list when you do not specify anything

ArcInfo command example Arc: USAGE CLEAN Usage: CLEAN <in_cover> {out_cover} {dangle_length} {fuzzy_tolerance}{POLY|LINE} Arc: CLEAN STREET STREET2 # # LINE

Getting help for ArcInfo Get Usage by typing the command No argument Good habit to do that Arc: BUILD Usage: BUILD <cover> {POLY|LINE|POINT|NODE|ANNO.subclass} Arc: COMMANDS ….. Arc: COMMANDS B BATCH BUFFER BUILD Getting help for ArcInfo commands  The easiest way to display a usage line is to type in a command name without any of its arguments and then press Enter. This practice is potentially dangerous because some commands (e.g., QUIT) execute without any arguments. You can use the USAGE command to avoid accidental execution of a command. Arc: BUILD Usage: BUILD <cover> {POLY|LINE|POINT|NODE|ANNO.subclass} The USAGE command provides an alternative way of displaying a usage line. Arc: USAGE <command> Notice that the result of the following example is identical to the result in the previous example. Arc: USAGE BUILD Usage: BUILD <cover> {POLY|LINE|POINT|NODE|ANNO.subclass} You can display complete or partial listings of available commands on the screen by asking for COMMANDS at any ArcInfo prompt (Arc:, Arcedit:, Arcplot:). Arc: COMMANDS The following example lists only those commands beginning with the letter B. Arc: COMMANDS B BATCH       BUFFER       BUILD The HELP command starts ArcInfo online documentation. Arc: HELP

ARC Macro Language (AML) Use to communicate with the ARC system Full programming capabilities ArcInfo commands + OS commands AML elements: Directives Functions Variables ARC Macro Language (AML)  The ARC Macro Language (AML) is the language through which you communicate throughout the ARC system. AML provides full programming capabilities and a set of tools to customize the user interface of your application. In addition to ArcInfo commands and operating system commands, AML files can contain other elements to execute actions during your ArcInfo session. You can use AML from an AML file or directly from the command line. There are two types of AML files: command macros and menus. Macros organize a sequence of ArcInfo commands into easily performed sophisticated geoprocessing operations. Menus provide an easy-to-use interface that employs a mouse to select desired menu choices. AML is a flexible language. You can combine host operating system commands, ArcInfo commands, and AML elements to perform complex operations. There are three types of AML elements: Directives Functions Variables

AML directives Instruct AML to perform a specific operation Start with an ampersand (&) Examples: Arc: &RUN my.aml Executes an AML program Arc: &MENU my.menu Opens an AML menu Arc: &TERM 9999 Sets the terminal type for AML menus Directives instruct AML to perform a specific operation. For example, you can use a directive to run an AML program or type a message to the screen. If a command begins with an ampersand (&), it is recognized as an AML directive. Examples: Arc: &RUN my.aml Executes an AML program. Arc: &MENU my.menu Opens an AML menu. Arc: &TERM 9999 Sets the terminal type for AML menus.

AML functions A function performs text substitution The function name appears in [] A function can return A number A character string A Boolean value Returned value can be used further Arc: BUILD [response ‘Enter the coverage to BUILD’] POLY Arc: BUILD [getcov * -line] A function performs text substitution. The name of a function appears within square brackets [ ]. When AML encounters the square brackets, it evaluates the function and returns the value of the function. Functions can return a number, a character string, or a Boolean value. Normally, the returned value is assigned to a variable or used as part of a command line. For example: Arc: BUILD [response 'Enter the coverage to BUILD'] POLY Displays the text 'Enter the coverage to BUILD', captures the user's response, and submits it to the BUILD command. Arc: BUILD [getcov * - line] Displays a scrolling list of all line coverages in the current workspace, captures the user's choice, and returns the name of the coverage to the BUILD command.

AML Variables A way to store dynamic information Variable types: Character strings Integers Real numbers Boolean expressions &SETVAR – to set a variable’s value Examples: Arc: &SETVAR COV = LANDUSE Arc: &SV COV [response ‘enter cov name:’] Arc: BUILD %COV% POLY A variable is a means of storing dynamic information. AML variables can be assigned a wide variety of data types: Character strings Integers Real numbers Boolean expressions The &SETVAR directive is used to set a variable. For example, the variable referred to as “COV” is assigned a value as follows: Arc: &SETVAR COV = LANDUSE or Arc: &SETVAR COV [response 'Enter the coverage to BUILD'] Percent signs (%%) are used to evaluate a variable. Arc: BUILD %COV% POLY

Summary Subsystems Data formats: raster and vector ArcInfo workspace, INFO directory Commands, ArcTools AML: directives, functions, Variables ArcDoc and Command Usage Summary  In this lesson, you learned which data formats ArcInfo supports, the basic structure of ArcInfo and its subsystems, and which subsystems you will be using in this course. ArcInfo supports both vector and raster data formats. You can use coverages (ArcInfo's basic unit of storage for vector data), DXF files, grids, images, TINs, and lattices with ArcInfo. A coverage includes spatial (location) data, topologic (where features are in relation to one another) data, and attribute (descriptive) data, linked together, for the geographic features it contains. Each individual feature in a coverage has a unique numeric identifier assigned to it; this identifier is stored with both the spatial data file and the attribute data file, ensuring a strict one-to-one correspondence between the spatial and attribute data. ArcInfo stores all of the geographic datasets in a special directory (folder) on your computer called a workspace. In addition to geographic data files, a workspace can contain AML macros and menu files, key legend files, and maps in the form of ArcInfo graphics files. The INFO database (which stores all feature attribute data) is stored in the Info subdirectory in the workspace. ArcInfo consists of the ARC, ArcTools, TABLES, ArcInfo LIBRARIAN, ARCPLOT, ARCEDIT, AML, and the ODE subsystems. Each subsystem manages a different set of functions. To perform tasks in ArcInfo, you can use several methods. You can enter commands at the program prompt, run AML programs, or use the ArcTools menu-driven interface. To get help when working with ArcInfo, access the online help system, called ArcDoc.

ArcInfo Data Coverages

Topology A mathematical procedure that determines these for geographic features Spatial properties Spatial relationships Spatial Relationship Spatial Property Each arc has a beginning node and an ending node Directionality and length of the arc Arcs connect to other arcs at nodes Connectivity Connected arcs form polygon boundaries Area and perimeter of polygon Arcs have polygons on their left and right sides Adjacency or contiguity Topology  Topology is a mathematical procedure that determines spatial properties and relationships of geographic features. It uses spatial relationships to define spatial properties.

Topology-Spatial Property ArcInfo uses the inherent topologic relationships of lines and polygons to provide extensive geographic analysis capabilities. A topologic data model builds polygons from the list of individual arcs that define their borders. The system stores arc coordinates only once because two polygons that are adjacent may share the common arc between them. A topologic data model therefore stores data efficiently and facilitates advanced geographic analysis. In contrast, a non-topologic data model stores each closed polygon as a single entity. The arcs shared by adjacent polygons must be entered and stored twice, either by double-digitizing or copying the arc. This duplicate data makes geographic analysis difficult because of the system’s inability to observe topologic relationships between polygons that share a common border. The non-topologic model is a common data model supported by some Geographic Information Systems (GISs) and many computer aided drafting (CAD), mapping, and graphics systems.

Arc-node topology Arc-node topology  Arc-node topology expresses the relationship between arcs (lines) and nodes (the beginning and ending points for arcs). It defines length, direction, and connectivity for arcs. Geographic analysis relies on these properties for accurate results. The length of an arc is the distance between its beginning node (from-node) and its ending node (to-node) measured in coverage units. Coverage units may be in digitizer inches at the start of the automation process, but they are usually converted to feet or meters when a coordinate system is chosen for the final database. The direction of an arc is defined by starting at the from-node (FNODE#) and moving toward the to-node (TNODE#). The direction of an arc is important only if an application requires directional modeling consistent with the from-to direction of the arc (e.g., applications that include rivers or traffic flow). Arcs connect if they share a node. In the illustration below, you can see that arcs with STREET#'s 4, 7, and 8 are connected because they each share node 8. Whether a node is a from-node or a to-node doesn't matter when determining connectivity.

Polygon-arc topology Polygon-arc topology  Polygon-arc topology expresses the relationship between arc features and the polygon features for which the arcs create boundaries; it defines area and adjacency. Geographic analyses for polygons rely on polygon-arc topology similar to the way arc analysis relies on arc-node topology. ArcInfo records and stores coordinate information about polygons as arcs (ARC files) and label points (LAB files). Each polygon contains a unique label point (the same feature that is used to create a point feature) and is linked to the identifiers of the arcs that enclose the polygon, which in turn are tied to coordinate data. When an arc or set of arcs connect to form a closed figure, the enclosure defines the area of a polygon. This set of arcs is stored as a list called the Polygon Arc List, or PAL file, defining the polygon or polygons they enclose. Polygons are adjacent if they share an arc. ArcInfo numbers polygons and stores them as left polygon (LPOLY#) and right polygon (RPOLY#). The same polygon can be the left polygon in relation to one arc and the right polygon in relation to another arc. In this slide, notice that polygon number 5 is the right polygon in relation to arcs 6 and 10, but it is the left polygon in relation to arc 14. You can visualize the concept of left and right polygons by imagining that you are traveling along an arc the same way you would drive along a road. Your starting point is the from-node and you are heading toward the to-node. The area to your left is the left polygon; the area on your right is the right polygon. When ArcInfo builds polygon–arc topology, it always creates one "universe" polygon to represent the area that lies outside your coverage. The arcs that establish the outer limits of your coverage polygon features define the inner limits of the universe polygon. The universe polygon is always POLY# 1.

Coverage features Coverages are either points, lines, or polygons A coverage can be both a line coverage and a polygon coverage Annotation Descriptive text associated with other geographic features E.g. street names, soil types Coverage features  ArcInfo stores geographic features as either points, lines, or polygons. Points are single x,y locations used to represent point features, such as wells and buildings. Lines (called arcs in ArcInfo) are a string of x,y locations used to represent linear features, such as roads, streams, and utility lines. Nodes are single x,y locations which occur at the ends and intersections of arcs. For example, traffic lights and manholes could be represented as nodes. Polygons are homogeneous areas enclosed by a boundary and used to represent areal features, such as parcels, flood zones, or soil types. ArcInfo supports the grouping of arcs and polygons into complex feature types, such as routes and regions. Routes are linear features composed of arcs, with a linear measurement system, such as transportation routes. Regions are areal features composed of one or more polygons. Examples of regions are wildlife habitat areas or parcels that change over time. Annotation is a unique feature type in ArcInfo. Annotation is descriptive text associated with other geographic features (e.g., street names and soil types).

Feature attribute tables FATs are INFO files Each object is associated with a record in an FAT A coverage may have more than one FAT (e.g. a PAT, AAT, & NAT) Feature Classes Feature Attribute Table Name Description Point <cover>.PAT Point Attribute Table Arc <cover>.AAT Arc Attribute Table Node <cover>.NAT Node Attribute Table Polygon Polygon Attribute Table Feature attribute tables  When ArcInfo constructs topology for a coverage, it defines and stores topologic and geometric properties in a file called a feature attribute table (FAT). There are four types of feature attribute tables, one for each main feature type. A feature attribute table name is composed of two parts, its prefix and its suffix (or extension). The attribute table prefix is named the same as the coverage, and its suffix represents the type of features contained in the attribute table. For example, a table named STREET.AAT contains the attributes for a line (arc) coverage named Street. The table below shows the extensions for the major ArcInfo feature types. Depending on the feature type, the contents of feature attribute tables differ; however, they all have some characteristics in common, including: They are INFO data files. Each feature in a coverage occupies one record, or row, of data in the feature attribute table. There can be more than one feature attribute table for a set of spatial data. For example, you might have polygon and arc attributes (e.g., lots and lotlines), or node and arc attributes (e.g., water lines and meters) in a single coverage. Later in this course, you will learn to edit feature attribute tables and feature coordinates.

Records and feature identifiers RECNO – internal record number COVER# - ArcInfo assigned ID COVER-ID – user assigned ID Records and feature identifiers  Each record in a feature attribute table has three identification numbers associated with it. Each record has a record number (RECNO), a unique number for the feature called Cover# (assigned by ArcInfo), and another feature identification number called Cover-ID (assigned by you, the user). In this course and in ArcInfo's documentation, the term "cover" refers to the name of an ArcInfo coverage. For example, if your coverage is named PARCELS, then Cover# and Cover-ID become PARCELS# and PARCELS-ID in the feature attribute table. RECNO is the internal record number assigned to each row of data in any INFO data file, including feature attribute tables. RECNO is a unique row identifier and a valid field, or column, for a database query. The Cover# is a unique number assigned by ArcInfo and used as the feature identifier. Values are sequential starting at 1 and increment by 1 for each feature. Each time data is added to or deleted from the coverage, values change. Cover# values always match the record number (RECNO) in the feature attribute table. The terms "Cover#" and "internal number" both refer to the ArcInfo feature identifier. You, the user, assign the Cover-ID. Because it is a feature identifier, most users assign it a unique number; however, it does not have to be unique. Cover-ID values are commonly based on a coding scheme and used as temporary attributes during data automation. Their values can be any positive integer but they do not have to be sequential. When data is added to or deleted from the coverage, Cover-ID values do not change. The terms "Cover-ID", "User-ID", and "ID" are used interchangeably throughout ArcInfo's documentation; all refer to your identifier for a feature.

Points Points  Point features are geographic features that can be thought of as single locations or occurrences and defined by a single pair of x,y coordinates. No length or area is represented. Benchmarks, wells, structures, wildlife sightings, and spot elevations are examples of point features. The point attribute table (PAT) is the type of feature attribute table ArcInfo creates when it constructs topology for a point coverage. The PAT contains four standard columns of attribute data, called ITEMS. You can add other items representing additional attributes to the right (only to the right) of the COVER-ID item. Standard PAT ITEMS: AREA—the area of each point is always zero; points have no area. PERIMETER—the area of each point is always zero; points have no perimeter. COVER#—the internal feature number that ArcInfo assigns for each point feature. It always matches the RECNO value and, like RECNO, changes each time data is added or deleted. COVER-ID—the user-defined feature identifier assigned when the point is digitized; it will not change when data is added or deleted. In ArcInfo, point and polygon attribute tables are both called PATs and have identical formats. However, it is easy to tell the difference between them because point attribute tables always have zero values for the ITEMS of AREA and PERIMETER. Because both feature types share the same attribute table, point and polygon features cannot be stored in the same coverage. ArcInfo automatically records and stores coordinate information about points in the LAB file as they are entered into the system. Coordinate files cannot be edited or displayed directly by the user; they are maintained using ARCEDIT.

Arcs Arcs  Linear geographic features are represented by arc features in ArcInfo. Arc features allow you to locate and describe geographic information that exists along a path between two points. Streams, roads, utility networks, and contour lines are examples of arcs. The beginning and ending points for an arc are called nodes (FNODE and TNODE respectively) and vertices, a string of x,y coordinate pairs, define the arc's shape. ArcInfo records and stores coordinate information about arcs as they are entered into the system. ArcInfo automatically converts every 500th vertex (the maximum number of vertices per arc) to a node and starts a new arc with a unique identifier. ArcInfo determines the x,y coordinates for each node and vertex using the coverage's coordinate system, then calculates the length for each arc. ArcInfo creates an Arc Attribute Table (AAT) when it constructs topology for an arc coverage. The AAT contains seven standard columns of attribute data, called ITEMS. Standard AAT ITEMS: FNODE#—the internal number of the node where the arc begins TNODE#—the internal number of the node where the arc ends LPOLY#—the internal number of the polygon on the left side of the arc RPOLY#—the internal number of the polygon on the right side of the arc LENGTH—the length of each arc in coverage coordinate units COVER#—internal feature number COVER-ID—user-defined feature identifier You can add additional attrtibutes to the AAT by attaching other items (attributes) to the right of the Cover-ID item. For a coverage with arc topology but no polygon topology, the values for the LPOLY# and RPOLY# are always zero (0).

Nodes Nodes  Nodes represent features that occur specifically and uniquely at the end points of arcs rather than as events along an arc. Nodes are also a distinct feature type as well as the endpoints of arcs. Nodes indicate the end points of arcs and cannot exist independently of an arc. The from-node (FNODE) is the first vertex in the arc and the to-node (TNODE) is the last vertex. Together, they define the direction of the arc. Stop lights, stop signs, railroad crossings, street intersections, and dams are examples of nodes. ArcInfo records and stores coordinate information about nodes as a single x,y coordinate pair when the arcs are entered into the system. ArcInfo arbitrarily assigns the arc number of one of the arcs connected to a node as the identifier that links the node to its coordinate location. If more than one arc shares the node, the arc with the lowest internal number is used. ArcInfo creates a node attribute table (NAT) when it constructs topology for a node coverage. The NAT contains three standard columns of attribute data, called ITEMS. Users can add to the NAT by attaching other descriptive data (attributes) about the nodes to the table. Standard NAT ITEMS: ARC#—the internal number of one of the arcs that intersects at the node COVER#—internal feature number COVER-ID—user-defined feature identifier ArcInfo attributes always appear to the left of the Cover-ID in the attribute table. User-defined attributes are added to the right of the Cover-ID in the table. If two arcs intersect, a node is placed at the intersection of the arcs, splitting the two arcs into four arcs. If the two arcs overlap but do not intersect (e.g., freeway overpasses), a node is not placed at the point of overlap. Geographic features that occur at points along arcs rather than at their intersections can be represented as events by the route system feature type, which will be discussed later in the module.

Polygons Polygons  Polygons represent geographic features having a homogeneous area within a boundary. Examples of polygons are parcels, soils, vegetation types, states, and flood zones. In ArcInfo, each polygon contains a unique label point (the same feature that is used to create a point feature) and is linked to the arcs that enclose the polygon using the unique arc identifiers stored in a Polygon Arc List (PAL) file. Area and perimeter for each polygon are calculated using the coordinate data stored in the ARC file. ArcInfo creates a polygon attribute table (PAT) when constructing topology for a polygon coverage. The PAT contains four standard columns of attribute data, called ITEMS. Users can attach other descriptive data (attributes) about the polygons to the PAT. Standard PAT ITEMS: AREA—the area of each polygon in coverage coordinate units PERIMETER—the perimeter of each polygon in coverage units COVER#—the internal feature number ArcInfo assigns for each polygon feature COVER-ID—the user-defined feature identifier. It is assigned when the label point for a polygon is digitized The first record in a PAT represents a special polygon—the area beyond the coverage—called the universe polygon. The universe polygon has the following characteristics: an area value that is the negative of the sum of all polygon areas in the coverage a perimeter value that is the sum of the perimeter of the bounding polygons of the coverage a COVER# value that is always internal feature number 1 a RECNO value of 1 a COVER-ID that is always 0 Because polygons are constructed using points, arcs, and nodes, there are some rules you need to know to construct them correctly. Point and polygon features cannot be stored in the same coverage because they use the feature (label point) and attribute table (PAT) to assign attributes. Each polygon label point should have a unique identifier. ArcInfo attributes are always to the left of the COVER-ID in the attribute table. User-defined attributes are always added to the right of the COVER-ID in the attribute table.

Features with subclasses Features with subclasses  There are some geographic phenomena that cannot be represented digitally as points, lines, or polygons. By extending the ArcInfo data model, geographic features that are composites of other features, geographic features that change over time, and geographic features of the same class that overlap can be included in a GIS and spatially analyzed. Regions and routes are feature classes that support the modeling of these types of features. Annotation is a unique feature type that stores text labels as text strings, along with their associated characteristics.

Routes A coverage can contain multiple route systems Each is a separate subclass Each is made up of sections Each section is made up of arcs or portions of arcs Routes  Route systems provide a means to model linear features with existing arc features. You can use a set of arcs representing linear feature locations to construct route systems that support any linear event occurring along them. A coverage can contain multiple route systems; each is a separate subclass, such as bus routes, trash collection routes, highways, pavement quality, speed zones, school bus routes, emergency vehicle routes, and so on. Subclasses of a route system represent multiple themes associated with one set of underlying arc features. For example, the same set of arcs can be combined or split in different ways to represent a bus route and a garbage truck route. A route system is a collection of routes, sections, and measures. Routes are made up of sections, and sections are made up of arcs or portions of arcs. Measures identify locations along the route. A route is an ordered collection of sections that represents a linear feature. It may be discontinuous or contain loops and forks.

Route events Events are located using the route’s measure units and the route contains sections that are associated to the arcs which contain the actual coordinate information. Sections are arcs or portions of arcs that form the building blocks of routes. Sections link the routes to the underlying arc features. Sections express the direction of and the measurement system for the route. Measures are positions along the route that are located using a measuring system based on linear measures (such as miles or time) as opposed to a two-dimensional x,y coordinate system. A route system uses this common system of measurement for storing and analyzing data. For example, you would say that a given shopping mall is five minutes from your house, instead of "The mall is located at 6835621, 1238584." The ability to locate events on linear features directly from attribute tables containing distance measures is called dynamic segmentation. The Dynamic Segmentation section in the ArcDoc contains more information on the concepts and commands that support routes and sections.

Regions Regions contain attribute information but do not contain spatial or coordinate information. Spatial information is determined from the underlying polygons that make up the region. Regions  The region feature class models areal geographic features consisting of one or more polygons. Using regions offers an extended approach to modeling complex areas. Regions make it possible, within a single coverage, to efficiently model overlapping polygons of the same class, a set of connected or noncontiguous polygons that comprise a single geographic feature, and nested polygons that combine to form one area at the next level up in a hierarchy. Examples of regions are census tracts containing census blocks, states containing counties, floor plans showing multiple building stories, tracking the shape of parcels as they change over time, toxic waste overlapping aquifers, and discontinuous wildlife habitat areas. A "void area" surrounds each region. The void area of a region may have discontiguous components. A hole within a region is considered part of the void area. A region subclass is a logical collection of region geographic features with its own set of attributes (e.g., a coverage "landcover" may have a subclass "forest" and a subclass "soil"). A coverage can have many regions and many regions can share the same polygon feature. Refer to Regions in ArcDoc for more information regarding the concepts and commands that support regions.

Annotation Is a feature type Does not represent geography of a feature Annotation  Annotation is text stored with a coverage that labels coverage features and enhances the interpretation and cartographic output of the data. Annotation differs from other ArcInfo feature types because it does not exist anywhere in the real world as a physical object or defined boundary. Annotation is, however, part of the geographic database and communicates important information about the other geographic features to the GIS user or map reader. Subclasses of annotation allow multiple sets of annotation (text) to be grouped together in one coverage. For example, you may want annotation showing parcel owners and annotation showing parcel areas to be accessed separately but stored together within one coverage. Is a feature type Does not represent geography of a feature Can be associated with other existing feature types Or as independent of any feature

Summary Topology in ArcInfo coverage Nodes, points, lines, polygons, regions, subclasses Summary  ArcInfo uses the topologic data model to determine the spatial relationships and properties of features. A topologic data model constructs polygons from the individual arcs (lines) that form their borders. Arc coordinates are stored only once because topology recognizes that two adjacent polygons share the common arc between them. The topologic data model therefore stores data efficiently and facilitates advanced spatial analysis. Spatial properties of arcs that can be determined from their spatial relationships are direction, length, and connectivity. Spatial properties determined from the spatial relationships of polygons are area, perimeter, and adjacency (or contiguity). Nodes are the beginning and ending points of arcs. An arc's beginning node is called the from-node and its ending node is the to-node. Arc-node topology expresses the relationship between arcs and their nodes and defines arc length, direction, and connectivity. Polygon-arc topology expresses the relationship between arcs and the polygon features created from the arc boundaries. ArcInfo assigns each polyon a unique label point that is linked to the identifiers of the arcs that enclose it. The set of arcs that encloses a polygon defines the polygon's area and is stored as a list called the Polygon Arc List, or PAL file. When ArcInfo constructs topology for a coverage, it stores topologic and geometric data for the coverage in a feature attribute table (FAT). There are four types of FATs: point attribute table (PAT), arc attribute table (AAT), node attribute table (NAT), and the polygon attribute table (PAT). Although point and polygon attribute tables have the same PAT file extension, you can easily distinguish them because the area and perimeter fields in the point attribute table always have zero values. Each record in a feature attribute table has three identification numbers associated with it: a record number (RECNO), a unique number assigned by ArcInfo called Cover# ("cover" is the coverage name), and a feature identification number called Cover-ID assigned by the user (again, "cover" is the coverage name). When ArcInfo constructs polygon-arc topology, it creates a universe polygon representing the area outside the coverage. The universe polygon is always called POLY#1 and is always the first record in the polygon attribute table. ArcInfo supports feature subclasses, including regions and routes. Annotation is a unique feature type that stores text labels and their associated characteristics as text strings.

Exercises Ex1 – Understanding spatial relationships Ex2 – Introduction to GIS functions Ex3 - Use the ArcInfo help system Ex4 - Operate ArcInfo (commands, AML) Ex5 - Operate ArcInfo (ArcTools)