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

Field Types

Split Policy Options

Merge Policy

Options

Coded Value Domain

Date, double, float, long integer, short integer, text

Default value, Duplicate

Default value

Range Domain

Date, double, float, long integer, short integer

Default value, Duplicate, Geometry ratio

Default value, Sum values, Weighted average

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 ofContents

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

SimpleTable objects exist independently of each other

CompositeDestination 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

Relate Join

Typical Uses Modeling and editing related objects

Querying, selecting

Querying, labeling, symbolizing

Referential Integrity

Yes No No

Messaging Yes No No

Attributes Yes No No

Relationship Rules

Yes No No

Cardinality All 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 GISTINs, 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 3rd 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