Thank you, Simon and Kirk, for entertaining my question. I'll search for high-resolution, local DEM data. I know lidar data is available. I'll ask specific questions once I get there.
Morgan On Wed, Oct 22, 2025, 8:31 AM Kirk Schmidt via QGIS-User < [email protected]> wrote: > Hi Morgan: > > This is an interesting question. I am assuming the gpx tracks do not > have elevation data, and if so, they may not have the accuracy needed > for the 12 inch delta in elevation. Also, the device you used to record > the daa may be optimized to minimize file size, therefore is is unlikely > you have usable elevation data in the gpx files. > > You need to generate a raster digital elevation model (dem) or access > one for your target area. In contrast to vector data, a raster is > typically a continuous grid and for elevation data, each grid would > contain the average elevation for that spatial location. So if each > cell in a dem is 10m x 10 m (30.49' x 30.49'), it would not be able to > find a flat area that is 100 ft2 (10' x 10'). This is referred to as the > resolution of the raster. > > If you can locate aerial lidar data for your area, the associated dem > typically has a high resolution and would meet your needs. You could use > the contour lines from a georeference map, however, you would have to > digitize the lines and you would be limited by the contour interval. If > it was 6", then you could find what you are looking for, if it is 5, 10 > or 30 feet, there would be too much approximation to reliable find flat > areas. The workflow would be to digitize or source the contour lines, > convert them to points at high density> use these to generate a raster > at a high enough resolution to find low slope contiguous cells that are > less than 100 ft2, so perhaps 2.5 to 3'. > > If you can source a high resolution dem, then you can generate a slope > raster from the dem and us that to find contiguous areas of 100 ' or > more that have a slope of less than 10 % (1 foot over 10 feet). > > This is a conceptual answer to your question. If you proceed, and can > source a high res dem, than re-ask the question and the group can > provide the specific steps to reach your gola. > > Kirk Schmidt > > > On 10/21/2025 9:27 PM, Morgan Fletcher via QGIS-User wrote: > > I use qgis mostly for visualizing gpx tracks, georeferencing old maps, > > drawing vectors to reveal or highlight information related to a map or > > physical location. > > > > I have a real-world need, a wish list item, and I wonder if QGIS might > > be able to solve it. > > > > I want to know where the flat spots are. Given a bounded area on a > > map, could I ask QGIS to find me all locations that are at least 100 > > square feet, with less then 1' vertical delta across that space? Yes, > > I'm trying to find flat camping spots. > > > > Morgan > > > > _______________________________________________ > > QGIS-User mailing list > > [email protected] > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > > -- > Kirk Schmidt, MScF, BScF, RPF > General Manager > Nortek Resource Solutions Inc. > 26 Church Road > Sutherlands River, NS > B0K 1W0 > Tel (902) 922.3607 > Email: [email protected] > Web: www.nortekresources.com > > _______________________________________________ > QGIS-User mailing list > [email protected] > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >
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