The system uses public Shuttle Radar Topography Mission (SRTM) version 2 data sourced from the NASA 2000 mission which is a modified dataset improved by the National Geospatial Intelligence Agency (NGIA).
The modifications removed erroneous spikes although the data still contains a small number of errors in extremely mountainous terrain. The global data is accurate to either 30 metres / 90 feet or 90 metres / 270 feet. The NASA data extends to 60 degrees latitude in both poles with extra polar data courtesy of Cartographer Jonathan De Ferranti BA (http://viewfinderpanoramas.org) who has carefully created the data. The data only depicts the earth’s surface and does not generally include man-made structures however large elongated concrete features (present in the year 2000) have been included. Tall ‘sky scrapers’ were smoothed out of the data as part of the version 2 data scrub but they can still be modelled with the addition of landcover or custom point clutter.