What: Have you noticed that the drawing time of a map increases with the number of raster layers used to symbolize it? This can be alleviated pretty easily. Why? It can get tedious waiting for your map to redraw. This is not always necessary -- here we describe how you can decrease the number of raster layers used on your map with no loss of visual quality. For the Crater Lake map, once we had elevation, bathymetry and vegetation (bump map) symbolized, we quickly got tired of how slowly it was drawing. Three raster layers were used to draw the elevation, three more were used to display the bathymetry and two were used to draw the vegetation. Even though we had trimmed the layers of the map down to the bare minimum, it was taking ten or more seconds to draw. By flattening out the raster layers, we were able to get the map to draw in a little under four seconds with no loss of cartographic quality. How: By flattening, we mean combining the content in these raster layers into one image, making it possible to draw the background of the map with one layer instead of what was ultimately nine layers (we also decided to flatten the buffered park boundary).
This effect works best for raster layers with no text -- if you flatten vector layers or text the linework will become pixellated, especially if you use a coarser resolution. Try this yourself with and without vectors and text to see the differences for your map.
Here's how to flatten the background raster layers:
An added benefit of flattening so many images was that we were able to decrease the size of the images in the data download for this map from over 120Mb to 6Mb (without pyramids, 18Mb with pyramids).
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