Introduction

Selecting features from a geographic layer or rows from a standalone attribute table is one of the most common GIS operations. Queries are created to enable these selections, and can be either attribute or spatial queries. Attribute queries use SQL statements to select features or rows through the use of one or more fields or columns in a dataset. An example attribute query would be "Select all land parcels with a property value greater than $500,000". Spatial queries are used to select features based on some type of spatial relationship. An example might be "Select all land parcels that intersect a 100 year floodplain" or perhaps "Select all streets that are completely within Travis County, Texas". It is also possible to combine attribute and spatial queries. An example might be "Select all land parcels that intersect the 100 year floodplain and have a property value greater than $500,000".