geoprocessing in arcgis issues • geoprocessing often involves areas or lengths, so using a...

5/1/2017

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Chapter 10

Geoprocessing

(Continued)

Copyright © McGraw-Hill Education. Permission required for reproduction or display.

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Geoprocessing in ArcGIS

Copyright © 2015 by Maribeth H. Price

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Geoprocessing• Executing analysis functions and tools

• Stringing together analysis functions to achieve a result


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Geoprocessing Environment

• Familiar ways to execute functions– Menus and toolbars

– ArcToolbox

• Environment settings

• New ways to execute functions– Command line

– Creating new tools with ModelBuilder

– Writing scripts


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Menus and Toolbars

• Quick access to common functions

• Organized by topic

• Turn off and on as needed

• Customizable

• Many different toolbars and menus available


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…..More!

ArcToolbox features

• Hundreds of functions organized into toolsets

• Expandable by purchasing extensions.

• Runs in ArcMap or ArcCatalog

• Many functions in the toolbox are not accessible from the menus and toolbars.

• Create custom toolsets with your favorite tools

• Create your own tools


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Environment Settings

• Environment Settings affect the output of tools and commands

• Set at application level or when running a tool

• Application level settings are saved with map documents


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Setting Environment Settings


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Application level settings affect all tools and menus

Tool settings affect one execution of one tool

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Some useful settings

• Current and scratch workspace

• Output coordinate systems

• Processing tolerances


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Use sparingly at first, and experiment with tool settings until you gain experience.

The XY tolerance

• Feature class property set at time it is created

• Minimum allowed distance between two vertices

• Used to cluster nearby vertices during geometry operations such as clip, intersect, etc.

• Default setting intended to preserve accuracy


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0.001 meter0.003281 feet0.0000000556 degrees

gap

overlap

ac

b

Clustering

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Using tolerances


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You can increase the XY Tolerance during geoprocessing to help eliminate slivers.

Value must be carefully chosen.

Affects the output only.

Effect of tolerances


10-121500 m1000 m

Default 500 m

Union performed on districts and counties using different tolerance settings

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Coordinate Systems and Geoprocessing

Issues• Geoprocessing often involves

areas or lengths, so using a projected coordinate system is usually required for best results.

• If not otherwise defined, the output CS defaults to the first data set input to the tool.

• Reprojections will be done during processing if needed, but it is better to control if they are done.

• A good analyst is always aware of the coordinate systems being used during processing.

Best Practices for Analysis• When developing a project,

choose a coordinate system, instead leaving data in a GCS or a chance mixture.

• Select a projection with minimal distortion for the study region.

• Convert all data sets to the same coordinate system (see Chapter 11) before doing any analysis.

• Ensure that the data frame is always set to the same CS as the data it contains.


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Background Processing

• Introduced in ArcGIS 10

• Allows you to continue working while a geoprocessing tool runs

• It is on by default

• Runs slower for short tasks but good for long ones

• Potential for file conflicts

• Author recommends turning it off


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Completion notification boxes:

Background processing

Foreground processing

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Geoprocessing options


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Turn off background processing here

Recently used tools

Using a tool


10-16Access info and Help

Error tips

Double-click

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Searching for tools

• Search window

• Find tools based on name or keyword


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See where tool lives

Click to open tool

Hover for description

Some analysis tools


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The Intersect tool


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Dissolving


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Choose to summarize

other attributes

One attribute preserved in

output

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The Buffer tool


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NONE option ALL option

Careful! The default Dissolve option on this tool is often NOT the best choice.

Lengths and areas of features


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Areas and lengths

• Areas or lengths are important

– Total length of streams in each watershed?

– Total snail habitat area?

• Often tools change areas or lengths of features


10-23Before After

Dissolve

Remember• Geodatabase Shape_Area and Shape_Length fields

are automatically updated.– Other fields may contain areas or lengths which are NOT

• Shapefiles do NOT update any area or length fields automatically.


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Updating lengths and areas

• After performing operations than can change geometry, such as clip or intersect, recalculate any user-defined length or area fields.


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Model Builder


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Geoprocessing• Executing analysis functions and tools

• Stringing together analysis functions to achieve a result


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ModelBuilder

• Create models built from sequences of tools

• Store processing steps for later reference

• Execute models repeatedly with different inputs

• Share models with others


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Building models


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1. Open new model

2. Drag and drop a tool from the toolbox to the model.

3. Open the tool and enter the parameters. 5. Done. Add another step if

needed

4. Run the model step

Creating a new toolbox


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Toolboxes may be created in folders, geodatabases, or in other toolboxes.

Name toolbox

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Add toolbox to ArcToolbox


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Although accessible from the Catalog, it is convenient to place the new toolbox in ArcToolbox.

Creating a model


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1. Create new model

2. Open Model Properties

3. Set Model Properties

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Adding tools to model


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1. Drag ‘n’ drop tool to model

2. Right-click to open tool properties

Manage model layout

Set tool arguments


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Colors indicate that tool is ready to run.

input tool output

Run

Shadow indicates the step has been run.

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Set Intersect arguments


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Select blue icons to ensure chain

of inputs , outputs

Set Intersect(2) arguments


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Set output properties


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Add to Display puts the output in the Table of Contents for viewing.

Intermediate indicates that the output is temporary. It will be deleted after tool completes running.

Model ready to run


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Examine Output


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Shadows indicate model has run.

Running it again

• Tools > Options > Geoprocessing– Set ArcMap to

overwrite existing datasets


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Run a model as a tool


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Setting an input to a parameter lets the user enter a value each time it is run.

Run as tool

Open canvas and edit

Parameters from tool arguments


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Models and Scripts

• Models can be converted to scripts (programs)

• Scripts can be written and edited separately from models

• Scripts can include looping, if-then control etc.

• Choose from several languages

• Python is used by ESRI for examples

• Another way to create your own tools


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geoprocessing in arcgis issues • geoprocessing often involves areas or lengths, so using a...

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