Map Services

The following overview of map services includes some things to keep in mind when investigating map services published by you or others, that you may wish to add.

Projection

The Map displays data using the WGS_1984_Web_Mercator_Auxiliary_Sphere (EPSG code/spatial reference ID 3857) projection, which is the map projection used by most online basemap services, including ArcGIS, Bing, and Google. Any map services that will be displayed as reference layers must be capable of being displayed in this projection. Dynamic ArcGIS map services can be reprojected on-the-fly; however, this does negatively impact performance. Performance will be best if you use map services published in the Web Mercator projection. Cached map services are typically only available in the projection in which they were cached.

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Cached Map Services

The best way to create fast map services is to cache them. With a cached map service, the server draws the map at a set of predefined scale levels and saves the images. When the server receives a request for a map, it's much quicker to return one of these cached images than to draw the map again. Caching is appropriate for basemaps and maps that don't change often.

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Dynamic map services

Layers published as dynamic map services can be rescaled and re-projected on the fly.

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Comparison: Cached vs. Dynamic map services

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