Introduction to Geographic Information Systems Fall 2013 (INF 385T-28620)

Dr. David ArcturResearch Fellow, Adjunct Faculty

University of Texas at Austin

Lecture 6October 3, 2013

Spatial Data andGeoprocessing

Outline Attribute extraction Feature location extraction Location proximities Geoprocessing tools ModelBuilder

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ATTRIBUTE EXTRACTIONLecture 6

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Attribute query extractionYou have tracts for

an entire state, but

wanttracts for one

county only

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Attribute query extraction Select tracts by County FIPS ID

Cook County = 031

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Attribute query extraction Cook County tracts

selected Export to new feature

class or shapefile

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Export selected features Right-click to export selected features

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Add new layer Cook County tracts

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FEATURE LOCATION EXTRACTION

Lecture 6

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Select by location Powerful function unique to GIS Identify spatial relationships between

layers Finds features that are within another

layer

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Select by location Have Cook County census tracts

but want City of Chicago only Can’t use Select By Attributes No attribute for Chicago

Use “Municipality” layer City of Chicago is a municipality within

Cook County

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Select by location Select “Chicago” from municipalities

layer

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Select by location Selection, select by location

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Export selected features

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LOCATION PROXIMITIESLecture 6

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Points near polygons Health officials want to know polluting

companies near water features

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Points near points School officials want to know what

schools are near polluting companies

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Polygons intersecting lines Transportation planner wants to know

what neighborhoods are affected by construction project on major highway

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Lines intersecting polygons Public works official wants to know

what streets or sidewalks will be affected by potential floods

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Polygons completely within polygons City planners want to know what

buildings are completely within a zoning area.

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GEOPROCESSING TOOLSLecture 6

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Geoprocessing overview GIS operations to manipulate data Typically take input datasets,

manipulate, and produce output datasets

Often use multiple datasets

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Common geoprocessing tools Analysis

Extract – clip Overlay – intersect and union

Data management Generalization – dissolve

General append merge

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Accessing tools Geoprocessing menu

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Accessing tools ArcToolbox

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Accessing tools Search window

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Clip vs. Select By Location Clip

Clean edges Looks good

Select By Location Dangling edges Better for geocoding

(chapter 8)

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Dissolve Combines adjacent polygons to create

new, larger polygons Uses common field value to remove

interior lines within each polygon, forming the new polygons

Aggregate (sums) data while dissolving

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Dissolve Create regions using US states

Use SUB_REGION field to dissolve Sum population

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Dissolve

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Dissolve results States dissolved to form regions Population summed for each region

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Append Appends one or more datasets into an existing dataset Features must be of the same type Input datasets may overlap one another and/or the

target dataset TEST option: field definitions of the feature classes

must be the same and in the same order for all appended features

NO TEST option: Input features schemasdo not have to match the target feature classes’ schema

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Append DuPage and Cook County are

combining public works and need a new single street centerline file.

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Append Append will add DuPage streets to

Cook County streets

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Resultant layer One street layer (Cook County) with all

records and field items

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Merge Combines multiple input datasets of

the same data type into a single, new output dataset Illinois campaign manager needs a single

voting district map but wants to preserve the original layers

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Merge

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Resultant layer New voting district layer

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Union Overlays two polygon layers

Resulting output layer has combined attribute data of the two inputs

Contains all the polygons from the inputs, whether or not they overlap

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Union Neighborhoods and ZIP Codes

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Union

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Union Better describes characteristics of a

neighborhood Central business district 15222 vs. 15219

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Union Attributes tables contain different fields

and data

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Union results

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New polygons with combined data

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Union vs. Merge vs. Dissolve

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Operation # Input Feature Classes

Change in Geometry

Schema Restrictions

Union Multiple Combines all input geometries

Includes all fields from all input feature classes; input tables do not have to be identical

Merge Multiple Combines all input geometries

Input tables must be identical; retains one set of attributes

Dissolve Single Combines feature geometries based on shared attribute values

N/A – single feature class schema

Intersect Computes a geometric intersection of

the input features Features (or portions of features that

overlap in all layers and/or feature classes) will be written to the output feature class

Inputs can have different geometry types

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Intersect City manager needs to know what

buildings intersect flood zones and wants the flood data attached to each intersecting building

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Intersect

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Intersect result Only building polygons that intersect

flood zones with combined data fields

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MODELBUILDERLecture 6

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ModelBuilder overview Models automate and string tools together Example: You have census tracts for a county

and want to create neighborhoods for a city Some steps are needed to create

neighborhoods Join a crosswalk table to the tracts map layer Dissolve tracts to create neighborhoods using

the dissolve column in the crosswalk Remove the join so that the model can be

rerun if necessary You run the model for this workflow with one

click of a button

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Starting map TIGER census tracts and municipalities

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Final map Tracts dissolved to create

neighborhoods

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Crosswalk table Neighborhood names

are not included with the census tracts, so a crosswalk table was created with the name of neighborhood for each census tract

Some neighborhoods are made of multiple tracts

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Set geoprocessing options Geoprocessing > Geoprocessing

Options

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Create a new toolbox Catalog

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Create a new model Right-click Toolbox > New > Model

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Add tool to model Add Join tool

To join crosswalk table to tracts…

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Set parameter for Join tool Joins crosswalk table to census tracts

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Model steps

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Add join

Dissolve Remove join

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Finished model

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Summary Attribute extraction Feature location extraction Location proximities Geoprocessing tools ModelBuilder

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