Geographic Information Systems

Background abouts Maps: Themes and Layers Example

Some maps show a number of different kinds of information and others show one piece of information. This information is the theme of a map and they are represented using different colors, patterns, or symbols. Examples of themes include roads, cities, parks, rivers and lakes. Themes are displayed as layers in the activity below.
Check and uncheck the checkboxes for the layers shown in the image below to see how the map on the right changes.

As you turn on layers higher up in the layer stack, more themes become visible in the map. In this example, the initial map starts with a satellite image of the southern part of the San Francisco Bay Area. When the checkbox for the Urban Areas layer (the bottom layer) is checked, the Urban Areas layer appears on top of the base image. When the checkbox for the Rivers layer (the middle layer) is activated, both the Urban Areas and the Rivers become visible in the map. Finally, when the checkbox for the Cities layer (the top layer) is turned on, all three themes are shown in the map.

Experiment with turning different layers on and off to see how the map changes.

TASK: Layers activity

Last Modified: Feb 20, 2019