Preparing Data for Analysis andPreparing Data for Analysis andAnalyzing Spatial Data/Analyzing Spatial Data/

GeoprocessingGeoprocessing

Class 11 Class 11 GISG 110 GISG 110

ObjectivesObjectives

Preparing and Analyzing DataPreparing and Analyzing Data

Geoprocessing tools and processesGeoprocessing tools and processes– Data ExtractionData Extraction– OverlayOverlay– ProximityProximity

Spatial AnalysisSpatial Analysis

ModelsModels

GeoprocessingGeoprocessingA GIS operation used to manipulate GIS dataA GIS operation used to manipulate GIS data

Allows for definition, management, and analysis of Allows for definition, management, and analysis of information used to form decisionsinformation used to form decisions

Accomplished with ArcToolboxAccomplished with ArcToolbox

Typical geoprocessing operation:Typical geoprocessing operation:1.1. Takes input dataTakes input data

2.2. Performs operation on dataPerforms operation on data

3.3. Returns the result of operation as output dataReturns the result of operation as output data

Preparing dataPreparing data

Common issues when preparing data:Common issues when preparing data:

Too detailed or generalized for your map Too detailed or generalized for your map scalescale

Not enough attributes, need to create and Not enough attributes, need to create and populatepopulate

Too much data Too much data

Geoprocessing toolsGeoprocessing tools

Analysis tools fall into 3 categories:Analysis tools fall into 3 categories:

Data extractionData extraction

OverlayOverlay

Proximity AnalysisProximity Analysis

Data extractionData extraction

Creating a new subset of features in one Creating a new subset of features in one feature class based on the geographic extent feature class based on the geographic extent of another feature class of another feature class

Two common processes include:Two common processes include:– ClipClip– DissolveDissolve

ClipClip

Extracts dataExtracts data

An operation that An operation that extractsextracts the the features from one layer that features from one layer that reside entirely within a boundary reside entirely within a boundary defined by features in another defined by features in another layerlayer

E.g., Clip roads to a county E.g., Clip roads to a county boundaryboundary

Clip ExampleClip Example

Clip roads in the state roads input layer (line Clip roads in the state roads input layer (line fc) using the county polygon as the cookie fc) using the county polygon as the cookie cutter to create an output layer (line fc) cutter to create an output layer (line fc) containing just roads in the countycontaining just roads in the county

Clip Usage Tips & FactsClip Usage Tips & Facts

The feature class that is having its features The feature class that is having its features clipped (INPUT) can contain points, lines, or clipped (INPUT) can contain points, lines, or polygonspolygons

The clip feature class, must be a polygon The clip feature class, must be a polygon feature classfeature class

The Output feature class will have the The Output feature class will have the attributes of the Input featuresattributes of the Input features

Large datasets = memory issuesLarge datasets = memory issues

DissolveDissolve

Simplifies dataSimplifies data

Process of removing Process of removing unnecessary boundaries unnecessary boundaries between features, such as edges between features, such as edges of adjacent map sheets, after of adjacent map sheets, after data has been captureddata has been captured

DissolveDissolve

Use Dissolve when you want to aggregate Use Dissolve when you want to aggregate features based on a specified attribute or features based on a specified attribute or attributesattributes

E.g., Create the sales regions layer by E.g., Create the sales regions layer by removing the boundaries between counties removing the boundaries between counties represented by the same salespersonrepresented by the same salesperson

Dissolve ExampleDissolve Example

US CountiesBefore Dissolve

US SubregionsAfter Dissolve

Create new subregions from dissolved census tracts, Create new subregions from dissolved census tracts, ZIP codes, or countiesZIP codes, or counties

Dissolve Usage Tips & FactsDissolve Usage Tips & Facts

Dissolve fieldsDissolve fields– Features with the same value (within a field) will Features with the same value (within a field) will

be aggregated (dissolved) into a single featurebe aggregated (dissolved) into a single feature

Multipart featuresMultipart features– May result from dissolveMay result from dissolve– A single feature that contains noncontiguous A single feature that contains noncontiguous

elements and is represented in the attribute table elements and is represented in the attribute table as one record (e.g., county does not share border as one record (e.g., county does not share border with other counties being dissolved)with other counties being dissolved)

Dissolve Usage Tips & Facts (cont.)Dissolve Usage Tips & Facts (cont.)

Summarizing attributesSummarizing attributes– Aggregated features can also include Aggregated features can also include

summaries of any of the attributes present summaries of any of the attributes present in the input features in the input features

Coordinate system of the outputCoordinate system of the output– The output from the dissolve function will The output from the dissolve function will

be in the same coordinate system as the be in the same coordinate system as the input feature class input feature class

OverlayOverlay

Identify overlaps between features in two Identify overlaps between features in two layers and create a data set in which the layers and create a data set in which the lines of overlap define new featureslines of overlap define new features

Two common processes include:Two common processes include:– UnionUnion– IntersectIntersect

UnionUnion

This tool builds a new polygon feature class This tool builds a new polygon feature class by combining the features and attributes of by combining the features and attributes of each feature classeach feature class

UnionUnion

This operation combinesThis operation combines

1.1. Features of a polygon input layer Features of a polygon input layer ++

2.2. PolygonsPolygons from an overlay layer from an overlay layer ==

3.3. Output layer that contains the Output layer that contains the attributes and full extent of attributes and full extent of both both layerslayers (polygon fc) (polygon fc)

Non-overlapping areas are Non-overlapping areas are included in the output data setincluded in the output data set

Union exampleUnion example

Union streams buffered 35 feet (polygon fc) Union streams buffered 35 feet (polygon fc) ++

Timber stand boundaries (types of timber, Timber stand boundaries (types of timber, oak, pine, etc. – also polygon fc) oak, pine, etc. – also polygon fc) ==

Portions of stands located within and outside Portions of stands located within and outside buffered streams (polygon fc)buffered streams (polygon fc)

Union Usage Tips & FactsUnion Usage Tips & Facts

All input feature classes and feature layers All input feature classes and feature layers must have must have polygonpolygon geometry geometry

The output features will have the attributes of The output features will have the attributes of all the input features that they overlapall the input features that they overlap

Output may be multipart (can change if not Output may be multipart (can change if not desired)desired)

Large datasets = memory issuesLarge datasets = memory issues

IntersectIntersect

Computes a geometric intersection of the Computes a geometric intersection of the Input FeaturesInput Features

Features or portions of features which Features or portions of features which overlap (intersect) in all layers and/or feature overlap (intersect) in all layers and/or feature classes will be written to the Output Feature classes will be written to the Output Feature Class Class

IntersectIntersect

This operationThis operation

1.1. Cuts an input layer Cuts an input layer ++

2.2. Features from an overlay layerFeatures from an overlay layer = =

3.3. Output layer with features that Output layer with features that have attribute data from have attribute data from both both layerslayers

Intersect Usage Tips & FactsIntersect Usage Tips & Facts

The Input Features must be simple features: The Input Features must be simple features: point, multipoint, line, or polygonpoint, multipoint, line, or polygon

If the inputs have different geometry types If the inputs have different geometry types (e.g., point on line), the Output Feature Class (e.g., point on line), the Output Feature Class geometry type will default to be the same as geometry type will default to be the same as the Input Features with the lowest dimension the Input Features with the lowest dimension geometry (point)geometry (point)

Intersect Usage Tips (cont.)Intersect Usage Tips (cont.)

The Output Type can be that of the Input The Output Type can be that of the Input Features with the lowest dimension Features with the lowest dimension geometry geometry or loweror lower

Output may be multipart (can change if not Output may be multipart (can change if not desired)desired)Large datasets = memory issuesLarge datasets = memory issues

Union and Intersect OutputUnion and Intersect OutputOutput contains the Output contains the attributes and full attributes and full extent of both layersextent of both layers

Only overlapping Only overlapping geometry is preservedgeometry is preserved

Features have attributes Features have attributes from both input layersfrom both input layers

Proximity AnalysisProximity Analysis

Finds what is near or within a certain Finds what is near or within a certain distance of one or more features distance of one or more features

Common process includes bufferCommon process includes buffer

BufferBuffer

This tool creates a new feature class of This tool creates a new feature class of buffer polygons around a specified input buffer polygons around a specified input feature (polygon, line, or point)feature (polygon, line, or point)

BufferBuffer

A zone around a map feature measured in A zone around a map feature measured in units of distance (or time)units of distance (or time)

Area drawn at a specified distance around a Area drawn at a specified distance around a featurefeature

Features lying inside the buffer have Features lying inside the buffer have different status from features lying outside different status from features lying outside the bufferthe buffer

How buffer worksHow buffer works

Buffer works in Euclidean space and uses a Buffer works in Euclidean space and uses a two-dimensional algorithmtwo-dimensional algorithm

A buffer will be the same width no matter A buffer will be the same width no matter what the coordinate system iswhat the coordinate system is

It will not reflect the curvature or the shape It will not reflect the curvature or the shape of the earthof the earth

For the best results, generate the buffer in a For the best results, generate the buffer in a map projection that minimizes distortion in map projection that minimizes distortion in the area of interestthe area of interest

How buffer works (cont.)How buffer works (cont.)

The buffer width can be specified in two ways:The buffer width can be specified in two ways:

Fixed distanceFixed distance: Specify a constant distance : Specify a constant distance to apply to the Input Features (OR)to apply to the Input Features (OR)

From fieldFrom field: Choose the name of a numeric : Choose the name of a numeric distance field from the specified feature distance field from the specified feature class. Each feature will be buffered class. Each feature will be buffered according to its associated value in the according to its associated value in the chosen field.chosen field.

Fixed distanceFixed distance

Buffer a line feature a distance of 20 (e.g. 20 Buffer a line feature a distance of 20 (e.g. 20 feet)feet)

Because the buffer distance is a constant, all Because the buffer distance is a constant, all features are buffered to the same width (20 features are buffered to the same width (20 feet) feet)

From fieldFrom field

Buffer a line feature using a numeric field Buffer a line feature using a numeric field with values of 10, 20, and 30 for Distancewith values of 10, 20, and 30 for Distance

Because the buffer distances are dependent Because the buffer distances are dependent on the field values, various buffer widths can on the field values, various buffer widths can be applied in the same operationbe applied in the same operation

Buffer ExampleBuffer ExampleOceanside Unified School District

Data analysis stepsData analysis steps

Typical analysis with geoprocessing Typical analysis with geoprocessing operations:operations:

1.1. Determine which geoprocessing tools you need (plan)Determine which geoprocessing tools you need (plan)

2.2. Determine the order in which the geoprocessing tools Determine the order in which the geoprocessing tools should be used (plan more – use workflow diagram)should be used (plan more – use workflow diagram)

3.3. Locate the first tool and open its dialog boxLocate the first tool and open its dialog box

4.4. Enter the tool parameters, including the input and output Enter the tool parameters, including the input and output datasetsdatasets

5.5. Run the tool, examine output and repeat if necessaryRun the tool, examine output and repeat if necessary

Spatial AnalysisSpatial Analysis

Problem solving in GISProblem solving in GISProcess of examining the Process of examining the locationslocations, attributes, and , attributes, and relationships of features in spatial data through relationships of features in spatial data through overlay and other analytical techniques in order to overlay and other analytical techniques in order to address a question or gain useful knowledgeaddress a question or gain useful knowledge– Use when need to solve a spatial or statistical Use when need to solve a spatial or statistical

problemproblemExtracts or creates new information from spatial Extracts or creates new information from spatial datadataTwo very useful spatial analysis tools in ArcToolbox: Two very useful spatial analysis tools in ArcToolbox: buffers and overlaysbuffers and overlaysRange from simple to complexRange from simple to complex

Sample spatial analysis applicationsSample spatial analysis applications

Overlaying layers — Overlaying different Overlaying layers — Overlaying different layers of features to create new information layers of features to create new information identifying the spatial relationships between identifying the spatial relationships between the inputs (union, intersect)the inputs (union, intersect)Identifying what is nearby — Finding what is Identifying what is nearby — Finding what is near a feature or the distance between near a feature or the distance between different types of spatial features (buffer)different types of spatial features (buffer)Quantifying the results — Presenting the Quantifying the results — Presenting the results of your analysis through statistical results of your analysis through statistical analysis or frequency countanalysis or frequency count

Spatial Analysis ExampleSpatial Analysis Example

Locating the number of Locating the number of public schools within public schools within 30 miles of a hospital30 miles of a hospital

1. Buffer hospitals by 30 miles

2. Select by location

3. Output: New layer or selected set

ModelsModels

ModelsModelsA collection of geoprocessing operations A collection of geoprocessing operations that automatically execute that automatically execute in sequencein sequence when when the model is run to produce a final outputthe model is run to produce a final output

Any geoprocessing operation in a model can Any geoprocessing operation in a model can be modifiedbe modified– The model can be run again to quickly The model can be run again to quickly

refine an analysis or produce new datarefine an analysis or produce new data

Workflow diagrams and modelsWorkflow diagrams and models

Workflow diagrams can be turned into Workflow diagrams can be turned into modelsmodels

ModelbuilderModelbuilder

ModelBuilder is the graphical environment in ModelBuilder is the graphical environment in which you create and interact with modelswhich you create and interact with models

The building block of a model is called a The building block of a model is called a processprocess– A process consists of a geoprocessing A process consists of a geoprocessing

tooltool

ModelbuilderModelbuilder

Color coded by Color coded by elementselements (input, values, and (input, values, and output) and output) and processesprocesses (or geoprocessing tool) (or geoprocessing tool) – White elements = not ready to runWhite elements = not ready to run– If If allall elements in process are colored = elements in process are colored =

ready to runready to run

ModelbuilderModelbuilder

To add a process to a model, find a To add a process to a model, find a tooltool in in ArcToolbox or ArcCatalogArcToolbox or ArcCatalog and drag it into and drag it into the modelthe model

Can also drag and drop Can also drag and drop datadata into a model into a model from ArcCatalog or ArcMapfrom ArcCatalog or ArcMap

ReviewReview1.1. Analysis tools fall into what three categories?Analysis tools fall into what three categories?2.2. Use Clip when you want to aggregate features based on a Use Clip when you want to aggregate features based on a

specified attribute or attributes. (T/F)specified attribute or attributes. (T/F)3.3. The clip feature class, must be a polygon. (T/F)The clip feature class, must be a polygon. (T/F)4.4. To perform a ______ operation, all input feature classes and To perform a ______ operation, all input feature classes and

feature layers must have feature layers must have polygonpolygon geometry. geometry. 5.5. List an example (or operation) for a proximity analysis?List an example (or operation) for a proximity analysis?6.6. In most cases, a buffer distance will vary depending on the type In most cases, a buffer distance will vary depending on the type

of coordinate system. (T/F)of coordinate system. (T/F)7.7. The first step in a typical analysis with geoprocessing The first step in a typical analysis with geoprocessing

operations is: Determine the order in which to run the operations is: Determine the order in which to run the geoprocessing tools. (T/F)geoprocessing tools. (T/F)

8.8. __________ diagrams (white in color) can be turned into __________ diagrams (white in color) can be turned into models.models.

9.9. The Modelbuilder is color coded by The Modelbuilder is color coded by ________________ (input, values, (input, values, and output) and and output) and ________________ (or geoprocessing tool). (or geoprocessing tool).

10.10. You can drag and drop tools and data into a model from You can drag and drop tools and data into a model from ArcCatalog and ArcMap. (T/F)ArcCatalog and ArcMap. (T/F)

Remainder of ClassRemainder of Class

BreakBreak

ESRI Chapter 11 ESRI Chapter 11 Preparing data for analysisPreparing data for analysis

(Dissolving, Creating graphs, Clipping, (Dissolving, Creating graphs, Clipping, Exporting)Exporting)

ESRI Chapter 12ESRI Chapter 12 Analyzing spatial data Analyzing spatial data

(Buffering, Overlaying, Calculating attribute (Buffering, Overlaying, Calculating attribute values)values)