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Goals
• Define a conceptually and computationally compatible definition of flat– one based on the perception of flat– can be applied globally
• Test the feasibility of open source software for conducting large-scale geographic analysis
• Produce a ‘flat map’ for the continental US– Eerr…I mean Kansas
The Flat Map:A Perception Approach To Modeling Flat Terrain
Joshua S. CampbellPhD Candidate - Geography
University of Kansas
GIS Day – 18 Nov 2009
Conceptual Flat
• Based on the human perception of flat– a terrain geometry interpreted by human
vision– can occur in association with any type of
landform (plains, river valleys, plateaus, glacial outwash...)
– is not tied to any specific geomorphic process, (erosion/sedimentation, aeolian/fluvial/glacial)
Calculate visibility at sea:
Visibility (in miles) = (1.17 x sqrt (height)) x 1.15
Height = 6 ft
Visibility = 3.3 miles or 5,310 meters
When does flat stop being flat?
A model of flat
Computation Flat
• Multi-neighborhood DEM analysis (90m SRTM)
• View to the horizon (3.3 miles)– 8 directions (N, NE, E, SE, S, SW, W, NW)– Minimum threshold of 0.32 degrees
• Local Slope (3 x 3 window: 270m) 0 - 3% slope = flat
5,310 meter view
30 meter rise
64-bit processing
GRASS Processing in QGIS
• r.in.gdal (55 times)• r.patch (mosaic)• g.region (change extents - tricky)• r.mapcalc (conditional statements: subset)• r.slope• r.horizon (8 directions)• r.recode (produce index layers)• r.mapcalc (sum: produce index)• r.statistics (zonal stats)• r.out.gdal (export to geotiff)
~2% of Kansas is flat
Thank You!
Presentation, KML files, and upcomingpaper will be available at my blog:
http://www.disruptivegeo.com