Attributes and Queries: An Introduction

Below are some typical questions that would be asked with spatial data:

• Which parcels are big enough for my house?
• Which areas have more poverty for development funds?
• Are environmental areas threatened by encroaching development?
• How many endangered species are in each area?
• How many fish are in each stream?
• Who borders the streams we need to restore?
• What areas have the most fire fuels (e.g. dead wood)?

To answer these questions, we need information:

• Size of parcels.
• Income levels for regions.
• Counts of species.
• Counts of people, animals, houses, etc.
• Height of trees, buildings, etc.
• Size and perimeter of areas.
• Length of streams or roads.
• Ownership of parcels.

This type of data can be found within the attributes of a shapefile.

Example: Census Scope

Census Scope is an organization that makes census information available. Navigate to this site and check out the variety of maps, charts, and tables they have made available from US Census Data. These are computed using attributes of the census data by county level (i.e. a polygon layer of counties).

Queries and Calculations

To answer the questions raised in Attributes: An Introduction, we also need to select (query) certain types of information, such as:

• People over 60 years old.
• Parcels over 1 acre.
• Areas with 1 or more endangered species.

And compute new values:

• Number of animals per meter.
• Density of trees.
• Board feet per acre.
• Fish per meter.

Attributes, Queries, and Calculations

Attributes are associated with features and are located within the Attribute Table. Queries "Select" data through the "Select by Attribute" tool, which is based on Structured Query Language (SQL). Calculations can be made through Calculate Geometry and Field (column) Calculator.

Each layer has a table attached to it, where each row is tied to a particular feature (point, line, or polygon) within that layer. Each column (field) represents a different attribute, such as: Name, type, or some other property.

The Attribute Table is similar to Microsoft Excel, in that each row is tied to a feature, you can add and delete columns, and adding and deleting rows will add or delete features.

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Additional Resources

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