Autodesk 15606-011408-9330 User Guide - Page 154

About Map Layers Layers are like separate transparent sheets on which your map data is drawn. Every map generally contains a minimum of one layer, but because layers are so useful for organizing and working with your data, a map typically will contain several layers. At minimum, you must have a separate layer for each type of data you use in the map. You cannot display points and polygons on the same layer, for example. You can create a layer and use it for a specific map, or save it as a separate Map Layer File (MLF) and use it in several different maps. A map can contain multiple layers of the same type, such as multiple polygon layers, each of which you can set up independently of the others. You can also create collections of related layers, called layer groups to help you organize layers in a map. You can create dynamic and static map layers. A dynamic layer stores only the layer styles (such as color, style, and symbology) in the Map Window File (MWF), not the map data, thus minimizing file size. When you access a dynamic map layer using Autodesk MapGuide® Author or Autodesk MapGuide Viewer, Autodesk MapGuide® Server sends the map data for the layer on demand. As you zoom in and out on the map, Autodesk MapGuide Server sends the data for the visible area only, not for the entire map. Dynamic layers are most appropriate for medium to large data sets and for maps that cover a large area. A static map layer stores a snapshot copy of the layer data for the entire Map Window and embeds it in the map file. Because all of the data is already in the map, the layer takes a little longer to load, but zooming in and out is faster than with dynamic layers, because no additional data needs to be downloaded from the server. Note that if you change the map's default center and size or map projection, Autodesk MapGuide Server must rebuild all static map layers, as it does with dynamic layers. Static map layers are most appropriate when the data set does not change often, the size of the data set is relatively small, and the map covers a small area. Also, because the data is contained within the map itself, static layers are best used when data security is not an issue. Autodesk MapGuide Author draws layers in order of increasing priority starting with priority 0, then priority 1 on top of layer priority 0, and so on, until it draws the layer with priority 100 last, on top of all other layers. The drawing order is reflected in the Autodesk MapGuide Viewer legend and in the Map Explorer, where the layer with the lowest priority is at the bottom of the list, and the layer with the highest priority is at the top of the list. 154 | Chapter 9 Working with Map Layers