6.4 Selection Methods: Select By Location vs. Select By Attributes

Selection Methods: Select By Location vs. Select By Attributes in ArcGIS Pro 3.x

Selecting features is the foundational prerequisite for nearly every analysis, editing, data extraction, and geoprocessing workflow in ArcGIS Pro. When a selection is active on a layer, subsequent geoprocessing tools (like Buffer or Calculate Field) will honor that selection, operating only on the selected features and ignoring the rest of the dataset.

The two primary mechanisms for isolating data are Select Layer By Attributes and Select Layer By Location. The EAPA_2025 exam will heavily test your ability to determine which tool to use, how to configure their parameters, and how to chain them together to solve complex spatial problems.

1. Select Layer By Attributes

Select By Attributes allows you to isolate features strictly based on their tabular values, utilizing Structured Query Language (SQL) to define the filtering criteria. It does not consider geometry or spatial position.

Clause Builder vs. SQL Mode

ArcGIS Pro 3.x provides a highly intuitive Clause Builder interface that allows users to construct queries using dropdown menus, eliminating the need to write raw SQL syntax. However, for complex queries, or for users comfortable with database administration, you can toggle the interface into SQL mode to write or edit queries directly.

Core SQL Operators & Wildcards

You must be able to identify correct SQL syntax for the exam.

• Standard Relational Operators: =, <>, >, <, >=, <= (Note: <> means 'Not Equal To').
• Logical Operators (AND / OR): Used to chain multiple conditions together.
  • AND requires that both conditions be true for a record to be selected (e.g., ZONING = 'Commercial' AND ACRES > 5).
  • OR requires that at least one condition be true (e.g., ZONING = 'Commercial' OR ZONING = 'Industrial').
• Pattern Matching (LIKE and Wildcards): Used for partial string matching in text fields.
  • The percent sign % represents zero, one, or multiple characters. For example, CITY_NAME LIKE 'San%' will successfully select 'San Diego', 'San Francisco', and just 'San'.
  • The underscore _ represents a single, required character. For example, PARCEL_ID LIKE 'A_1' matches 'A11' and 'A91', but not 'A1' or 'A111'.
• The IN Operator: Used to efficiently select multiple specific values without writing chained OR statements. Example: STATE_ABBR IN ('CA', 'OR', 'WA').
• Null Values: To find empty fields, you must use IS NULL or IS NOT NULL. You cannot use = NULL.

Exam Tip: Text strings must always be enclosed in single quotes 'Text', while numeric values must not have quotes 99. Date fields depend on the underlying database but often require specific date formatting functions.

2. Select Layer By Location

Select By Location ignores attribute tables entirely and selects features based on their spatial, topological relationship to features in another layer (the selecting layer).

Common Spatial Relationships (Match Options)

Understanding the nuances of these spatial rules is critical:

• Intersect: This is the default and most permissive option. It selects target features that share any part of their geometry with the selecting features. If they overlap, touch boundaries, or contain each other, they are selected.
• Contains / Completely Contains: The target feature must encompass the selecting feature. "Completely Contains" is a stricter rule; the boundary of the inner feature cannot even touch the boundary of the outer feature.
• Within / Completely Within: The exact inverse of Contains. The target feature must fall inside the selecting feature.
• Are Identical To: The geometries must be perfectly identical, occupying the exact same X,Y space.
• Boundary Touches: The features share a boundary (like adjacent parcels) but do not overlap in their interiors.
• Within a Distance: Selects features that fall within a specified straight-line buffer distance of the selecting features (e.g., selecting all schools within 500 feet of a highway).

3. Chaining Selection Operations

A powerful aspect of data extraction in ArcGIS Pro is the ability to chain operations together sequentially using the Selection Type parameter. This applies equally to both Attribute and Location selections, allowing you to build highly complex queries step-by-step.

Selection Types:

• New selection: The default behavior. It clears any currently active selection on the layer and creates a fresh selection based on the new criteria.
• Add to the current selection: Keeps existing selected features active and adds the new features to the set. This is functionally equivalent to a logical OR operation.
• Remove from the current selection: Unselects features from the currently active selection that match the new criteria. This is functionally equivalent to a logical NOT operation.
• Select subset from the current selection: Applies the new query only to the currently selected features, narrowing down the results. This is functionally equivalent to a logical AND operation.

Step-by-Step Scenario Example

You are tasked with finding large commercial parcels (target layer) that intersect a flood zone (selecting layer).

1. Step 1 (Select By Attributes): Open the Select By Attributes tool on the Parcels layer. Set the query to ZONING = 'Commercial' AND ACRES > 10. Set the Selection Type to New selection. You now have 500 large commercial parcels selected.
2. Step 2 (Select By Location): Open the Select By Location tool. Set the Input Features to Parcels and the Selecting Features to the Flood Zone layer. Set the Relationship to Intersect. Crucially, set the Selection Type to Select subset from the current selection.
3. Result: The tool only evaluates the 500 currently selected commercial parcels, determining which of those intersect the flood zone, narrowing your final selection down to perhaps 45 highly vulnerable parcels.

4. Persisting Selections

Selections are highly volatile; they exist only in active memory. If you click the map accidentally with the Explore tool, your selection will be cleared. To save your work, you must persist the selection:

• Make Layer From Selected Features: Creates a temporary, in-memory layer in the Contents pane based on the selection. This is fast but does not physically copy data.
• Export Features: Permanently exports the selected features to a new, physical feature class in a geodatabase. This is the safest way to store isolated data for permanent analysis.
• Save as Layer File (.lyrx): Saves a file that points to the original data and stores the SQL definition query, but does not duplicate the heavy spatial data on the hard drive.