A base map is a layer with geographic information that serves as a background. A base map provides context for additional layers that are overlaid on top of the base map. Base maps usually provide location references for features that do not change often like boundaries, rivers, lakes, roads, and highways. Even on base maps, these different categories of information are in layers. Usually a base map contains this basic data, and then extra layers with a particular theme, or from a particular discipline, are overlaid on the base map layers for the sake of analysis.
Some base maps look like Vector Layers but are actually tiled Raster layers. Tiled images are used because they display faster and deliver a good combination of layers for providing context and orientation. If your base map has raster layers, you cannot turn the layers off and on.
For example, if you wanted to show all the different types of endangered plants within a region, you would use a base map showing roads, provincial and state boundaries, waterways and elevation. Onto this base map, you could add layers that show the location of different categories of endangered plants. One added layer could be trees, another layer could be mosses and lichens, another layer could be grasses.
In the top right corner of the Viewer map, there is a base map control allows you to choose between at least two base maps:
The Base Maps or Map Themes drop-down list
Streets and Imagery Base Maps
Some base maps look like Vector Layers but are actually tiled Raster layers. Tiled images are used because they display faster and deliver a good combination of layers for providing context and orientation. If your base map has raster layers, you cannot turn the layers off and on.
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