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The best things in life are free, but only in that you do not have to pay cash for them. They definitiely demand committed effort.
Lack of maps has been a basic problem for people who are researching or working in areas that are not well mapped, or where the maps do not address our needs. Since 2003 there has been remarkable progress in the amount and quality of data available, and the kind of software--open source or commercial--that can handle the data.
TOPOGRAPHY. For topography there are two sources of raster data: National Oceanic and Atmospheric Association (NOAA) and NASA's Shuttle Radar Topography Mission (SRTM). NOAA has issued three series of increasing accuracy, from ETOPO5 (5-minute) to ETOPO2 (2-minute) to GLOBE (30 arc-seconds of coverage, which means 120 pixels/degree). The SRTM data-set is ten times the GLOBE resolution, providing a 3 arc-second resolution which is about 90 meters at the equator. This is more useful for local maps.
SURFACE COLOR. For surface character there is the NASA's Blue Marble series, in particular the massive 21,600 pixels x 10,800 pixels composite file which is 60 pixels/degree (1 arc-minute of coverage), and is 174 MB as an uncompressed TIFF file. This is a true-color image of the earth's surface overlaid on a shadow-cast of topography. The true-color imagery comes from the MODIS sensor on the Terra satellite.
For vector line data, there is the vmap0 series from NIMA, which supercedes
the CIA's WGS data. The Mapability
site is the best place to both review the nature of this data and to find the
links to download it. Mathworks
also provides information on the format. In issue 3 of GRASS
News, Markus Neteler describes how to extract vmap0 data either into ESRI's
shapefile format or import it directly into GRASS. It is also possible to extract
the data using Windows software (see the Mapability
site), but either method seems difficult; so to save you some grief I have posted
the three groups of data I have extracted:
Europe and North Asia (v0eur, 54 MB),
South Asia and Australia (v0sas, 58.5 MB),
South America and Africa (v0soa, 47.8 MB)
[The fourth region is North America (v0noa), and I have not extracted this data.]
Projection: LongLat
Datum/Spheroid: WGS84
Extracted categories:
- airports
- built-up areas
- canals and aqueducts
- coastlines
- ocean and sea bathymetry
- political boundaries
- railroads
- roads
- watercourses.
Page updated: 16 January 2005