Spatial Analysis Lab (SAL)

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Selecting Data and Creating Selection Layers


See also Using Wild Cards to Select Features


A Selection Layer creates a new layer out of set of selected features. This is not an actual new data layer, but a 'virtual' layer or subset of the original dataset. Both the number of features and the number of records in the attribute table are limited to only those features/records that were selected when the Selection Layer was created. Below are a few tips on different methods of selecting data (e.g., Select by Attribute and Select by Location) and how to create a Selection Layer. See also notes on Definition Queries.


By default, all features are shown for a data layer added to ArcMap (e.g., countries and/or cities in the example below)


To select features based on some attribute value from the attribute table, choose Select By Attributes from the Selection menu


In the Select By Attributes sheet, choose the Layer you wish to perform a selection query upon


Choose the Method of selection (typically a new selection, but alternatively a subset of already selected features, etc.)

Use the buttons to enter a SQL query for the data (or type it into the lower box)

Use the Get Unique Values button to show the values of a field

OPTIONAL: Use the Verify button to test your query syntax

Click OK to apply the selection query


The selection is made (both in the features and in the table)


To select features based upon their spatial relationship to another layer choose Select By Location from the Selection menu


Choose the type of selection to make


Choose the layer (or layers) to choose from

Choose the type of spatial relationship to use for the selection


Choose the layer to compare with (to be selected by)

If you have made a selection in this layer already, you can use just the Selected Features, or all features

Click Apply


Click Close to close the Select By Location sheet


For clarity, un-select the country layer selection by right-clicking on the layer name and choosing Clear Selected Features from the Selection context menu


Result: The cities that were located within the selected country are now selected


To preserve this selection subset, right-click on the layer in the Table of Contents and choose Create Layer From Selected Features from the Selection context menu


A new Selection Layer is added to the map (turn off the original cities for clarity)


OPTIONAL: Rename the Selection Layer if desired...


OPTIONAL: Right-click on the layer and choose Open Attribute Table


Note that the attribute table only contains those cities which were selected...





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