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