jm + garmin   1

This topographic map represents Ireland. It is designed for "hillwalking". The contour lines are extracted from SRTM public data provided by NASA. These files contain a digitized ground represented by points. The sample rate defines a grid resolution for Ireland around 90m in northing and 60m in easting. In major cases, digitized points do not correspond with summits. Carrauntoohil (1039m, the highest summit of Ireland) does not appear in SRTM data. The altitude reaches only 1018m.
Data were obtain from space with a radar. Because of the relative position between the radar and the earth, a shadow appears in some conditions (along ridges, behind summits...). This shadow matches with a gap in data (Imagine you with a flashlight in a dark room. It is hard to see what is in shadow). To close these gaps, you need other data or you can do interpolation. The second solution is applied in our case. There is one square degree per SRTM file with a sample rate of 1200x1200 points/square degree at Ireland latitude. [...]
All in all you obtain contour lines pretty sufficient for walking.
hillwalking  walking  ireland  gps  garmin  open-data  srtm  maps  hiking  via:alan 
november 2014 by jm

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