Tuesday, October 15, 2013

A Remedy for Your Basemap Blues

Problem: Slow Maps

So you are on a search and rescue mission using ArcGIS Desktop and while panning and zooming around the map, you are continuously waiting for basemaps to "re-draw". You can't guarantee an internet connection so you want to utilize your local data.

 Solution: Basemap Layers

Some nerdy GIS talk from the help documentation: "Basemap layers are a kind of map layer that provides a framework onto which you display your dynamic operational information. Basemap display performance is very fast. Since basemap layers are relatively static and do not change frequently, their display can be computed once and reused many times. The first time you visit an area at a particular map scale, basemap layer display is computed. The display is recalled on return visits to that area and map scale."

It is FAST! So let's get started.

Step one - Cartography

So this step will vary based on what you use as basemaps for your area. A long time ago Liz Sarow from Esri showed me how to make a nice hill-shaded topo from publicly available data. For California here are some resources:

1) Topos available as Digital Raster Graphics
2) 30m Digital Elevation Models available as Images (or these can be made with any DEM using the Hillshade tool)

The next trick is to add these to your map and style appropriately. I personally use a hillshade-on-topo "sandwich" - but I set hillshade properties as transparency of ~55% and Resample to bilinear interpolation.

Map sandwich!

Step two - Add a New Basemap Layer

Right-click the data frame name in the table of contents and click New Basemap Layer.

Adding a new basemap layerThe new basemap layer in the table of contents

Step three - Select the Layers 

Select the layers that will comprise your basemap and drag them into the basemap layer.Now you have a topo map that also highlights the terrain in your area - more importantly we can now pan and zoom around the map without waiting for redraw.

Please see the help document for more information. You can download my example as a tile package here and the try the steps above.

Other recommendations

  • Create these and store them for your areas of operational responsibility so they are ready to go ahead of time. These can be stored locally and remotely using Dropbox or ArcGIS Online.
  • Do not add any vector layers to your map that you plan on tracing for editing or clicking for attributes - this removes data access. No big deal if you do, just remember to pull the layers back out of the Basemap layer when you need them.
  • Whenever possible - use ArcGIS Online basemaps, they render quickly and feature more often updated content than your old topo and trail maps. See the World Topo Community Basemap and Open Streetmap 
  • RTFM Read the Free Manual: there are lots of other tips & tricks you can use in the ArcGIS Help documentation. Also - join our discussion group and ask the SARGIS geeks yourself! 

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