Intention

The vision of Maps-For-Free is to offer free worldwide relief maps and other layers which can easily be integrated into existing map projects.

MFF-maps are released under Creative Commons CC0. You are free to adapt and use the relief maps and relief layer for commercial purposes without attributing the original author or source. Although not required, a link to maps-for-free.com is appreciated.

SRTM

SRTM (Shuttle Radar Topography Mission) was developed to collect three-dimensional measurements of the Earth's surface to generate a near-global digital elevation model (DEM). The mission was a cooperative project between the National Aeronautics and Space Administration (NASA), the National Geospatial-Intelligence Agency (NGA) of the U.S. Department of Defense (DoD), and the German and Italian space agencies.

SRTM flew on board the Space Shuttle Endeavour in February 2000 and used an interferometric radar system to map the topography of Earth's surface. Endeavour was launched in an orbit with an inclination of 57 degrees which allowed to map all of the Earth's landmass that lies between 60 degrees North and 56 degrees South.

SRTM data was processed into geographic tiles, each of which represents one by one degree of latitude and longitude. A degree of latitude measures 111 kilometers North South, a degree of longitude measures 111 kilometers East West or less, decreasing away from the equator. Each tile of this dataset contains 1201x1201 samples which is equipollent to a 90 m grid resolution at equator. All tiles together represent an image sized 432000 x 139200 pixel.

For technical reasons data are available between 60 degrees North and 56 degrees South latitud only. The relative horizontal accuracy is about ± 15 m, the relative vertical accuracy about ± 6 m. The original data came with data voids indicating insufficient contrast in the radar data. These data voids tend to occur over water bodies (lakes, rivers, coasts, etc.), areas with snow cover and in mountainous regions.

The original SRTM data are available from USGS.

GTOPO30

GTOPO30 is another free geographic dataset with a resolution of 43200 x 21600 pixel used to cover regions where SRTM data are not available. Streaky regions denote areas where data voids were extrapolated or where SRTM data were replaced by the lower resolution GTOPO30 data.

The relief maps are elevation maps, i.e. the coloring does not reflect the natural colors of scenic objects. Because one color is used for each ground level, some rivers and other objects may appear in unnatural colors. Lowland areas containing only few elevation information appear most likely single-colored.

In some cases the SRTM or GTOPO30 dataset failed to include small islands, and in other cases the islands are slightly mispositioned.

The GTOPO data are also available from USGS.

VMap0

VMap0 provides worldwide coverage of geo-spatial data and is equivalent to a scale of 1:1000000. The data are structured following the Vector Product Format (VPF) and can be downloaded from GIS-Lab. Most of the MFF-layers are based on one of the thematic data vmap0 layer.

Hans Braxmeier, Donaustraße 13, 89231 Neu-Ulm, Germany, [email protected], 01-01-2017