GTECH 361 Lecture 10 Behavior and the Geodatabase

Rules and Behavior..is what makes geodatabase features smart Enforcing integrity with attribute domains Grouping features using subtypes Table relationships Between feature classes Between feature classes and non-spatial tables

Attribute Domains Define what values are allowed for a field in a feature or a non-spatial table Created and edited in ArcCatalog

Attribute Domains Are a specialization of well-known data types ValveTypeDomain is a Long Integer with a permissible value range from 1..10

Enforcing Data Integrity Preventing errors during data entry Checking validity after the fact

Types of Attribute Domains Range domains Coded value domains

Split and Merge Policies Use attribute domains to specify how attributes are handled after the split or merge Manage attributes that will be affected by edits to a feature's geometry

Split Policies Duplicate Default value Geometry ratio

Merge Policies Default value Sum Weighted average

Field Type Limitations to Split and Merge Policies

Subtypes The closest we get to object-orientation in the geodatabase To group similar features without creating a new feature class Group parcels into residential, commercial, and agricultural subtypes and associate different attribute domains with each group Faster than many feature classes

Subtypes in ArcGIS Versions ArcView Only displays subtypes ArcEditor, ArcInfo Create, edit and use subtypes

Example of a Subtype Subtypes of feature class country_lanes

Example of a Subtype Subtype encoding and decoding Feature class table ArcMap Table of Contents

Creating a Subtype Based on an existing attribute, or A new field containing subtype values Values have to be short or long integer For each subtype, you can associate default field values and domains You have to define one default type Once defined the new subtype can become target of an ArcMap edit operation

Using Subtypes with Features

Everything is Related… to everything else but… (Tobler’s Law) This multitude of relationships is usually not well captured in a GIS database Which makes tracking real-world situations difficult For instance…

Cardinality

Relationships Across Tables

Relationship Definitions Require primary and foreign key to be of the same type Supported field types are short integer long integer float double text object ID

Relationship Classes Permanently stored in the geodatabase Hence different from joins and relates in ArcMap, which are only stored in.mxd Within but not across geodatabase(s) Once created cannot be modified If corresponding table is deleted, the relationship class is deleted automatically Only 2 tables can be related per R.C.

Relationship Properties Cardinality, origin and destination tables As discussed before Labels Relationship types and messaging Attributes

Relationship Labels Relationship classes have forward and backward path labels

Relationship Types Simple Table objects exist independently of each other Composite Destination objects cannot exist without an origin object Forward messaging only One-to-one or one-to-many cardinality

Relationship Attributes Relationship classes can have attributes describing the relationship E.g, in a relationship between parcels and owners, an attribute of the relationship may be the percentage of ownership

Relationship Classes, Relates and Joins Relationship Class RelateJoin Typical Uses Modeling and editing related objects Querying, selecting Querying, labeling, symbolizing Referential Integrity YesNo Messaging YesNo Attributes YesNo Relationship Rules YesNo Cardinality All One-to-one, many- to-one

Relationship Rules Control how records in the origin and destination tables can be related Which objects or subtypes from the origin table can be related to which objects or subtypes in the destination table Specify a valid cardinality range for related objects or subtypes

Relationship Rule Example Wood poles are able to support from 0 to 3 transformers, whereas steel poles support 0 to 5 transformers

In Summary Modeling closer to real world by creating attribute domains, subtypes, and relationship classes Attribute domains define the allowable values Subtypes provide a way to implement different domains and relationships Relationship classes create a permanent record of their relationship (as opposed to join/relate) Relationship rules control which objects or subtypes from the origin table can be related to which objects or subtypes in the destination table

3-Dimensional GIS TINs, DEMs and 3-D Surfaces

Surface Analysis in GIS Analyzing the distribution of a variable which can be represented as the third dimension of spatial data Elevation is a good example of a 3 rd dimensional variable Most GIS packages represent z-values as an attribute of the data

What is a DEM? DEM = digital representation of a topographic surface (usually a raster or regular grid of spot heights) DTM or digital terrain model = more generic term for any digital representation of a topographic surface, but not widely used DEM is the simplest form of digital representation of topography and the most common Resolution is a critical parameter

Creating DEMs From contour lines (digital or scanned) scanning, raster to vector conversion + additional elevation data are (i.e. shorelines provide additional contours) algorithm is used to interpolate elevations at every grid point from the contour data

Creating DEMs By photogrammetry (manually or automatically) extraction of elevation from photographs is confused when the ground surface is obscured e.g. buildings, trees DEMs from each source display characteristic error artefacts

Background of TINs Developed in the early 1970's as a simple way to build a surface from a set of irregularly spaced points … Commercial systems using TIN began to appear in the 1980's as contouring packages, some embedded in GISs

Surface Analysis in a Vector GIS Several ways of building a TIN are possible: from a set of irregularly-spaced points from points in a regular fashion - a lattice from digitized contours as line features Not usually practical to use polygon features

The TIN Model Sample points are connected by lines to form triangles Each triangle's surface would be defined by the elevations of the three corner points Pros and cons of TINs

TIN Construction

From Points to Surfaces

Exaggerating Elevations

Terrain Analysis in Concert With Other GIS Operations

Calculating Slope and Aspect From (raster) DEMs: to estimate these at a raster point, a 3x3 window centered on the point is usually used From TINs: simpler and more efficient, but perhaps not as accurate

What Is Slope?

Slope and Aspect Calculation

Determining Drainage Networks A raster DEM contains sufficient information to determine general patterns of drainage and watersheds Flow direction determined by the elevations of surrounding cells Algorithms to determine the flow direction Water is assumed to flow from each cell to the lowest of its neighbors

DEM Flow Direction

Leading to Flow Accumulation

Flow Directions Accumulating Flow Critical Flow Level 2 Three Steps in Developing a Hydrological Model

Very Important Points

Relief Shading

2D elevation raster Transparent hillshade Shaded relief map Different Techniques for Visualizing Elevation

Main Uses of DEMs and TINs Determining attributes of terrain elevation at any point, slope and aspect Finding features on the terrain drainage basins and watersheds, drainage networks and channels, etc. Modeling of hydrologic functions energy flux and forest fires