Saturday, November 12, 2005

Maps: topographical, historical, free

It doesn't take much to realize that maps are the bread and butter behind the GPS adventure. Products usually lock customers behind proprietary formats to get a regular supply of sales. Nothing new there.

Most of these maps are based on the work of the United States Geological Survey (USGS) which either makes them available for download for free or charge a fee for large size requests.

There you can obtain topographical maps in paper, or their scanned counterparts in Digital Raster Graphics (DRG) format. Digital Elevation Models (DEM) can be used with DRG's to produce 3D maps as described in this great tutorial (check the toolbox and the list of freeware tools available to do this job).

In the vector based domain you can find Digital Line Graphs (DLG's), plus Geographic Names Information System (GNIS) gives you access to names of locations covered by these maps.

You can use public available tools to visualize maps with these type of data, like DLGV32 Pro which is a limited version of the commercially available Global Mapper.

Satellite Photos

USAPhotoMaps provides a fast and easy way to access satellite photos as Digital Ortho Quarter Quadrants (DOQQ) from USGS and the Microsoft TerraServer. It requires the download of a client software that runs on Windows. With it you can save .jpg image files and then transfer to a PDA. But be sure to push the contrast of these images, otherwise they won't look sharp enough in the small screen.

If you have a dedicated GPS like the Garmin models, you can upload data directly to it. Digital Data is another provider of satellite photos and BLM maps.

Not so free maps

But there are also companies that provide maps compatible with formats required by specific applications. That is the case of Chartiff, which sells maps for Fugawi, Memory Map and MapTrails among others.

In fact, the Bureau of Public Lands sells maps produced and distributed by Chartiff, including South California with its MapTrails software package.

TopoZone is another provider that will charge for shaded relief, satellite and street maps. Their service is built on top of the OpenSource MapServer project.

Historical Maps

MapTech which provides maps for OutdoorNavigator also hosts a series of historical maps from the turn of the 1900's mostly of areas in the East Coast. These maps seem to cover the same quadrants of today's topographical maps (at least that's the case for the Central Park map in New York City). You can select maps by cities, counties or an interactive map.

MapTech doesn't sell printed copies of these maps but refer you to Map Express which also sells printed copied of custom versions of topographical maps.

Books on Mapping and Maps

O'Reilly published two map related books that provide a great deal of tips and information about how to access, create and produce maps from freely available resources. If you use Linux both "Mapping Hacks" and "Web Mapping Illustrated" which covers MapServer usage in particular will give you lots to explore.