Return to Outline Copyright © 2009 by Maribeth H. Price 1-1 Chapter 1 GIS Data

Return to Outline Copyright © 2009 by Maribeth H. Price 1-2 Outline GIS Concepts –Representing the world as a mapRepresenting the world as a map –Coordinate systemsCoordinate systems –Modeling feature behaviorsModeling feature behaviors –Data quality issuesData quality issues About ArcGIS –Storing data in ArcGISStoring data in ArcGIS –Using ArcCatalogUsing ArcCatalog –Layers and layer propertiesLayers and layer properties

Return to Outline Copyright © 2009 by Maribeth H. Price 1-3 Representing the world as a map

Return to Outline Copyright © 2009 by Maribeth H. Price 1-4 How maps portray the world Point features Line features Polygon features Annotation features

Return to Outline Copyright © 2009 by Maribeth H. Price 1-5 Generalization Errors Neighborhood in Portsmouth, VA Courtesy GoogleEarth/Digital Globe USGS Digital Raster Graphic

Return to Outline Copyright © 2009 by Maribeth H. Price 1-6 Generalization and Scale Scale is the ratio of size on the ground to size on the map Scale influences the generalization of features About 1:24,000 About 1:50,000,000

Return to Outline Copyright © 2009 by Maribeth H. Price 1-7 Generalization and Scale Polygons at one scale may be points or lines at a different scale Large scale map Intermediate scale map Small scale map

Return to Outline Copyright © 2009 by Maribeth H. Price 1-8 Source scale and display scale Most GIS data have an intrinsic scale inherited from the source Display scale varies 1:24,000 USGS Topo Map

Return to Outline Copyright © 2009 by Maribeth H. Price 1-9 GIS data models Vector model Raster model

Return to Outline Copyright © 2009 by Maribeth H. Price 1-10 Vector model Vertices Polygon Points Nodes Line X Y Features are stored as a series of x-y coordinates in a rectangular coordinate system. Features can have one of three geometry types: points, lines, or polygons.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-11 Features and attributes Each feature is linked to an entry in a data table containing information about the feature—its attributes.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-12 Feature Classes A feature class is a collection of similar objects with the same attributes, stored as a single unit. Stored as spatial features with a table of associated attributes for each feature. Because all features must share the same table, all must have the same attributes. Feature classes may contain only one type of geometry (points or lines or polygons). States feature class Capitals feature class Rivers feature class

Return to Outline Copyright © 2009 by Maribeth H. Price 1-13 Vector data models Georelational model –Features and attributes stored separately –Linked by a common feature ID –Original model for older GIS systems Object-oriented model –Features and attributes are stored as a single unit –Reduces overhead in matching features to attributes –Simpler and helps maintain data integrity For the general user, the difference is negligible.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-14 Advantages of vectors Precise location of features Storing many attributes Flexible for cartography Compact storage of information Ideally suited for certain types of analysis, especially areas, lengths, connections

Return to Outline Copyright © 2009 by Maribeth H. Price 1-15 Storing surfaces Contours Raster TIN

Return to Outline Copyright © 2009 by Maribeth H. Price 1-16 Triangular Irregular Networks TINS are composed of nodes and edges which define triangular facets. All facets define orientations describing the surface. y z x (x,y,z)

Return to Outline Copyright © 2009 by Maribeth H. Price 1-17 Digital Elevation Model A DEM has cells or pixels, each of which contains a single elevation. Regularly spaced array of elevation values.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-18 The raster data model Rows Columns X, Y location Raster data file N rows by M columns X, Y location Georeferenced to earth’s surface

Return to Outline Copyright © 2009 by Maribeth H. Price 1-19 Continuous data Raster is the best way to store continuously changing values such as elevation or distance Analysis faster and more flexible than vectors for many applications Some analysis only possible using rasters

Return to Outline Copyright © 2009 by Maribeth H. Price 1-20 Discrete rasters Discrete rasters essentially store features—but in raster format Have relatively few values that change abruptly from one category to another roads land use

Return to Outline Copyright © 2009 by Maribeth H. Price 1-21 Continuous rasters Continuous rasters store surfaces or fields of variables that change continuously over space Many potential values. Adjacent cells rarely share the same value. Air photo DEM

Return to Outline Copyright © 2009 by Maribeth H. Price 1-22 Scanned images Paper maps recorded on a scanner form rasters also. This is a scanned USGS topo map, called a Digital Raster Graphic, or DRG. Discrete or continuous?

Return to Outline Copyright © 2009 by Maribeth H. Price 1-23 Picture files Any map picture file could potentially be used as a GIS data source. The picture must be georeferenced, or registered to a known coordinate system, before using in a GIS.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-24 Value raster vs picture raster A value raster such as a DEM or land use raster stores a value representing an object or quantity, like elevation or rainfall Used for analysis A picture raster stores arbitrary color values that have no direct relation to quantity or attribute Used as background pictures only

Return to Outline Copyright © 2009 by Maribeth H. Price 1-25 Impact of resolution Storage space increases by the square of the resolution Portraying large areas at high precision is problematic 90m resolution 10m resolution

Return to Outline Copyright © 2009 by Maribeth H. Price 1-26 Storage of attributes Roads may have other attributes: ownership, speed limit, number of lanes, etc. Would need a new raster for each attribute Only numeric attributes may be stored Raster contains 1 value indicating a single attribute— road type for example

Return to Outline Copyright © 2009 by Maribeth H. Price 1-27 Raster analysis functions Density Least cost path DistanceInterpolation Viewshed Buffers

Return to Outline Copyright © 2009 by Maribeth H. Price 1-28 Coordinate systems

Return to Outline Copyright © 2009 by Maribeth H. Price 1-29 Coordinate Systems Every GIS data set uses x, y, and sometimes z values to locate geographic data The choice of values is the coordinate system Data set is said to be georeferenced Vertices Polygon Points Nodes Line X Y X, Y location

Return to Outline Copyright © 2009 by Maribeth H. Price 1-30 X-Y Coordinate systems/units: Longitude-latitude (degrees) State Plane (feet) UTM (meters) Some familiar coordinate systems can be found on a topo map.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-31 UTM Zone 13 GCS State Plane Same point— different x-y’s

Return to Outline Copyright © 2009 by Maribeth H. Price 1-32 Coordinate systems and data Every feature class or raster stores x-y values based on a specific CS The feature class has a label documenting the CS parameters The label is critical for proper function of the feature class in ArcGIS ROADS , , , STATE , , ,649200

Return to Outline Copyright © 2009 by Maribeth H. Price 1-33 Modeling feature behaviors

Return to Outline Copyright © 2009 by Maribeth H. Price 1-34 Modeling feature behavior Constructing data models that mimic real-world situations –If two streets cross, the lines should meet at an intersection. –If an overpass crosses a street, the lines should not intersect. –Two adjacent states should have a single identical boundary between them. nodes Coincident boundary

Return to Outline Copyright © 2009 by Maribeth H. Price 1-35 Topology Topology describes the spatial relationships between features –Adjacency –Connectivity –Overlap –Intersection nodes Coincident boundary gap overlap

Return to Outline Copyright © 2009 by Maribeth H. Price 1-36 Logical consistency Describes how well the features mimic the real-world situations Usually confined to testing for topology errors gap overlap dangle loop Improper intersection Fig Topological errors can occur when editing is not carefully performed. undershoot overshoot pseudonode

Return to Outline Copyright © 2009 by Maribeth H. Price 1-37 Topology rules Shannon County Bennett County Pine Ridge Indian Reservation South Dakota Nebraska Topology rules establish how features should be spatially related. Topology rules may apply within a feature class or between feature classes. No gaps or overlaps between counties The Pine Ridge and Bennett County boundaries should match (overlap) The South Dakota and Pine Ridge boundaries should match These three layers show several topology errors.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-38 Vector model types Spaghetti models –Features stored as simple geometry objects –No topology stored –No way to test for topology errors –Manage errors by careful construction and editing of features Topological models –Features may be stored as simple objects –Complex features may be constructed from simpler ones –Supports complex feature behaviors such as network flow –Has rules and tools for defining topology and correcting errors

Return to Outline Copyright © 2009 by Maribeth H. Price 1-39 Data quality issues

Return to Outline Copyright © 2009 by Maribeth H. Price 1-40 Data Quality Data sets are rarely perfect No absolute quality standard Quality is defined as the fitness of a data set for a particular purpose Same data set may be unsuitable for one use but adequate for another User has ethical and legal responsibility to determine if a data set is sufficient for its intended use

Return to Outline Copyright © 2009 by Maribeth H. Price 1-41 Geometric accuracy Is it where it says it is? –Level of error in original source –Additional errors incurred or propagated during processing

Return to Outline Copyright © 2009 by Maribeth H. Price 1-42 Thematic accuracy How accurate are the attributes? –Tree crown density How is it measured? How accurate are the measurements? What are sources of error? Percent crown cover Density A 0-40% B 40-70% C %

Return to Outline Copyright © 2009 by Maribeth H. Price 1-43 Resolution Sampling interval of measurements –Spatial sampling Distance between GPS points along a road Size of pixel for elevation or satellite image raster –Thematic How fine was the measuring scale? Were the data classified after measurement? –Temporal How frequently were data sampled? Daily, monthly, every decade?

Return to Outline Copyright © 2009 by Maribeth H. Price 1-44 Precision Number of significant digits in a measurement Statistical variability of a repeated measurement NOT the same as accuracy! GPS unit reports locations to the nearest meter (precision: 1 meter) 20 GPS measurements at same spot have a standard deviation of 5 meters. (precision: about ±10 meters)

Return to Outline Copyright © 2009 by Maribeth H. Price 1-45 Metadata Contains information about data that people need to understand the data and evaluate its quality Should be provided with every data set distributed to the public Advised for in-house data as well

Return to Outline Copyright © 2009 by Maribeth H. Price 1-46 About ArcGIS Chapter 1. GIS Data

Return to Outline Copyright © 2009 by Maribeth H. Price 1-47 A history of products Arc/Info Arc ArcPlot Info/Tables ArcEdit GRID ArcView 3x ArcGIS ArcMap ArcInfo Workstation ArcCatalog ArcToolbox ArcGIS Desktop CoveragesShapefilesGeodatabases

Return to Outline Copyright © 2009 by Maribeth H. Price 1-48 ArcGIS Desktop ArcCatalog ArcMap ArcToolbox

Return to Outline Copyright © 2009 by Maribeth H. Price 1-49 ArcGIS functionality Three levels of functionality and cost $$$ArcInfo $$ArcEditor $ArcView Same interface and programs More tools in the toolbox

Return to Outline Copyright © 2009 by Maribeth H. Price 1-50 ArcGIS Extensions Spatial Analyst 3D Analyst Publisher/ArcReader Network Analyst Maplex Geostatistical Analyst Extensions are additional tools and commands that can be added to the core ArcGIS interface Appear as new toolbars and toolsets in ArcCatalog

Return to Outline Copyright © 2009 by Maribeth H. Price 1-51 Licensing Floating point licenses –ArcInfo only –Central server checks out licenses –Requires a dongle and a license file Standalone licenses –Uses a registration file/ register online –No dongle needed –Available for ArcView and ArcEditor only

Return to Outline Copyright © 2009 by Maribeth H. Price 1-52 Storing data in ArcGIS

Return to Outline Copyright © 2009 by Maribeth H. Price 1-53 Data formats CoveragesShapefilesGeodatabases

Return to Outline Copyright © 2009 by Maribeth H. Price 1-54 Shapefiles Shapefiles in Windows Explorer Shapefiles in ArcCatalog Coincident boundary Georelational One feature class Multiple files Simple features Spaghetti model Dbf tables From ArcView

Return to Outline Copyright © 2009 by Maribeth H. Price 1-55 Coverages Georelational model Topological model Multiple feature classes Many files Info tables From Arc/Info Usable in ArcGIS but not recommended Cannot be edited in ArcGIS A B

Return to Outline Copyright © 2009 by Maribeth H. Price 1-56 Coverage storage -Coverages have many tables stored in INFO database format -Tables store x-y values, attributes, and topology -Each feature has unique ID number linking it between tables Point table (x-y values) Arc table (x-y values) Node attribute table (NAT) Arc attribute table (AAT) Point attribute table (PAT) Polygon attribute table (PAT) Arcs are strings of xy coordinates Nodes are endpoints of arcs Polygons are built from arcs and a label that stores the attributes

Return to Outline Copyright © 2009 by Maribeth H. Price 1-57 Storing arcs Arc table Arc attribute table Arcs have a direction indicated by the order of x-y pairs

Return to Outline Copyright © 2009 by Maribeth H. Price 1-58 Connectivity A shared node indicates that the arcs are connected Arcs have direction indicated by from-to nodes May be different from x-y order (flipped arc)

Return to Outline Copyright © 2009 by Maribeth H. Price 1-59 Area definition A shared arc indicates that the polygons are adjacent

Return to Outline Copyright © 2009 by Maribeth H. Price 1-60 Contiguity

Return to Outline Copyright © 2009 by Maribeth H. Price 1-61 Polygon-arc topology PolygonArcs 26 25,107,108, , 99,142,143, ,174,143,181 Arc 107 x,y … 3 feature classes Each has table Shared node indicates connectivity Shared arc indicates adjacency

Return to Outline Copyright © 2009 by Maribeth H. Price 1-62 Geodatabases Object-oriented data model Topological data model Single file Multiple feature classes Several formats Feature datasets Simple and topological features Validation rules Customized object behavior

Return to Outline Copyright © 2009 by Maribeth H. Price 1-63 Geodatabases Designed to store feature classes for a particular geographic area Incorporates all feature classes, rasters, and tables within a single model Feature datasets Feature classes

Return to Outline Copyright © 2009 by Maribeth H. Price 1-64 Three types Personal geodatabases –Stored in a Microsoft Access database format –For single users or small workgroups –2 GB size limitation on feature classes File geodatabases –Stored as files in a geodatabase folder –For single users or small workgroups –Platform independent SDE geodatabases –Stored in a commercial RDBMS* (Oracle, SQLServer) –Designed for multiple users and large workgroups –Supports multi-user editing, versioned editing, etc. –Requires DBMS license and ArcSDE to translate data back and forth. *Relational Database Management System

Return to Outline Copyright © 2009 by Maribeth H. Price 1-65 What goes in GDBs? Feature classes Feature datasets –(collections of related feature classes) Tables Annotation Rasters Planar topology classes –Rules about how feature classes interact spatially Network topology classes –Enables modeling and analysis of network features

Return to Outline Copyright ©2006 by Maribeth H. Price 1-66 Functional applications Geodatabases support a variety of data management functions to enhance work –Domains and Subtypes –Planar topology and spatial rules –Network topology and connectivity rules –Relationships –Versioned editing (SDE geodatabases)

Return to Outline Copyright © 2009 by Maribeth H. Price 1-67 Domains Rules about what can go in attribute fields Reduces data entry and consistency errors Coded domains Set up a list of allowable values Range domains Set up a range of allowable values Pipe size: 1”, 3”, 6” or 12”Percent: 0-100

Return to Outline Copyright © 2009 by Maribeth H. Price 1-68 Subtypes Integer-coded classes of features Automatic display with different symbols Each subtype can have own default values Streamlines attribute entry

Return to Outline Copyright © 2009 by Maribeth H. Price 1-69 Planar topology Set up rules within and between layers –Must not overlap –Must not have gaps –Must not self-intersect, etc. Use during editing to ensure topologic consistency between features and feature classes Align county, state, and reservation boundaries

Return to Outline Copyright © 2009 by Maribeth H. Price 1-70 Network topology Create networks to analyze traffic, utilities Connectivity rules –12” pipe connects to 6” pipe only through adapter Find pathTrace downstream

Return to Outline Copyright © 2009 by Maribeth H. Price 1-71 Versioned editing SDE geodatabases only Allow multiple users to edit geodatabases simultaneously Can resolve conflicts between edited versions Can test “what-if” scenarios Can roll back to previous versions in case of failures

Return to Outline Copyright © 2009 by Maribeth H. Price 1-72 Other types of data Rasters Tables Layer files CAD Drawings

Return to Outline Copyright © 2009 by Maribeth H. Price 1-73 Important Although Windows permits spaces in file and folder names, in GIS they are a BAD IDEA. They often work, but sometimes a certain program or function will fail if it encounters a space in a folder name. Real GIS users FLINCH when they see spaces anywhere in folder/file names— even when they’re allowed!

Return to Outline Copyright © 2009 by Maribeth H. Price 1-74 Using ArcCatalog

Return to Outline Copyright © 2009 by Maribeth H. Price 1-75 The ArcCatalog Interface Folder tree Display window Menu/tool bars

Return to Outline Copyright © 2009 by Maribeth H. Price 1-76 Connecting to folders Shortcuts to frequently used folders or servers Must be added for drives other than C:\

Return to Outline Copyright © 2009 by Maribeth H. Price 1-77 Three view modes ContentsPreviewMetadata

Return to Outline Copyright © 2009 by Maribeth H. Price 1-78 Contents mode Viewing mode Large icons List Details Thumbnails

Return to Outline Copyright © 2009 by Maribeth H. Price 1-79 Metadata mode User can view metadata to evaluate data quality User can create, edit, import, or export metadata Create Edit Update Import Export Fig. 22. The metadata toolbar lets you create, view, and edit metadata for your layers.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-80 Preview mode - Geography Zoom In Zoom Out Pan Full Extent Previous/Next Extent Identify Create Thumbnail Tools

Return to Outline Copyright © 2009 by Maribeth H. Price 1-81 Preview mode – Table

Return to Outline Copyright © 2009 by Maribeth H. Price 1-82 Tables in ArcCatalog

Return to Outline Copyright © 2009 by Maribeth H. Price 1-83 File Properties Right-click file name Properties are controlled and set in ArcCatalog Different data types have different properties

Return to Outline Copyright © 2009 by Maribeth H. Price 1-84 Common Properties Coordinate system Create or correct label Fields Add or delete fields Attribute and spatial indexes Create index to speed queries

Return to Outline Copyright © 2009 by Maribeth H. Price 1-85 Layers and layer properties

Return to Outline Copyright © 2009 by Maribeth H. Price 1-86 About Layers A layer is a spatial data file together with a set of properties such as symbols, labels, etc. Created in ArcCatalog as a layer file Properties may be modified and stored

Return to Outline Copyright © 2009 by Maribeth H. Price 1-87 Creating a layer Right-click feature class and choose Create Layer

Return to Outline Copyright © 2009 by Maribeth H. Price 1-88 Layer properties Layers reference the original feature class— they do NOT store it Changing properties affects only the layer, not the original feature class If the original source is moved or deleted, the layer file won’t work

Return to Outline Copyright © 2009 by Maribeth H. Price 1-89 General properties Layer Name need not match layer file name. Use something descriptive. Display scale range is used to control at what scales a layer is drawn.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-90 Display scale range Visible range set less than or greater than a specific scale. Helps avoid clutter. 1:260,425 1:325,582

Return to Outline Copyright © 2009 by Maribeth H. Price 1-91 Symbology properties Used to control the symbols used to display the layer. Many different display options are available. Click to open the Symbol Selector and change the symbol

Return to Outline Copyright © 2009 by Maribeth H. Price 1-92 The Symbol Selector Symbols are stored together in groups called styles 1.Choose a symbol. 2.Modify its properties. 3.Expand symbol choices by choosing additional styles.

Return to Outline Copyright © 2009 by Maribeth H. Price 1-93 Definition Query 1.Query cities for capitals 2.Choose star symbol Cities layer Capitals layer

Return to Outline Copyright © 2009 by Maribeth H. Price 1-94 Group Layers Store multiple layers together as a group layer Edit properties of member layers separately

Return to Outline Copyright © 2009 by Maribeth H. Price 1-95 Label properties Create instant labels for a layer Uses algorithm to avoid overlaps Control font size, style, and label placement

Return to Outline Copyright © 2009 by Maribeth H. Price 1-96 Dynamic Labels Turn on/off for entire layers Redrawn each time the map view changes Uses Autoplacement to ensure no overlaps between labels Unavoidable overlaps are discarded Can specify placement properties

Return to Outline Copyright © 2009 by Maribeth H. Price 1-97 Placement properties

Return to Outline Copyright © 2009 by Maribeth H. Price 1-98 Placement Options polygons points lines

Return to Outline Copyright © 2009 by Maribeth H. Price 1-99 Point placement options Choose preferred locations Set up angled text Set treatment of duplicate labels

Return to Outline Copyright © 2009 by Maribeth H. Price Polygon placement options

Return to Outline Copyright © 2009 by Maribeth H. Price Line placement options Lines

Return to Outline Copyright © 2009 by Maribeth H. Price Scale range for labels

Return to Outline Copyright © 2009 by Maribeth H. Price Choosing label styles