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  • Using Overlapping Data

    Virtually all useful maps, whether paper or electronic, display overlapping map data. For example, streets typically overlay city limits areas. Also, identifying annotation may overlap some map features. We call each type of map data in the map legend a layer. Map layers overlap like transparencies (or sheets of pasta in lasagna!). Well-designed paper maps order overlapping layers so maps both look good and work well for their intended purposes.

    With MapGuide and many other electronic maps, users interact with the maps and adjust map information by panning, zooming, and:

    • Turning layers on and off in the stack of overlapping layers.
    • Seeing identifying map tips (those yellow pop-ups) for individual map features on the top layer.
    • Double-clicking on map features on the top layer to get more information.

    By turning layers on and off, MapGuide users add and remove overlapping map data.

    Understanding overlapping map data is essential to getting the most out of MapGuide as well as helping ensure you see what you need on the map. Using MapGuide, there are two ways that overlapping data may be in your map view.

    1. Overlapping layers - Most MapGuide users soon learn that displayed legend layers are on top of each other based on their order in the legend. One or more layers over a layer that is lower in the legend can interfere with viewing the lower layer which is "underneath" displayed layers higher in the legend. Since layer overlapping is fundamental to most MapGuide map viewing, it's important to understand the implications.

       

       

    2. Overlapping data in a layer - In relatively rare but important cases, there can be overlapping data in one displayed legend map layer. Special techniques are needed to learn how to understand and identify map features for layers that contain overlapping data. The techniques are important as there may be more mapped in the layer than what you "see" on the map.

       

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    Geographic Information Systems

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