- show topography or using elevation contour lines Topic: Topographic Maps.
Topographic Maps vs DEM. Topographic Map 1:24,000 Scale 20 ft contour 100 ft contour Stream Center...
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Transcript of Topographic Maps vs DEM. Topographic Map 1:24,000 Scale 20 ft contour 100 ft contour Stream Center...
Topographic Map1:24,000 Scale
http://www.tnrcc.state.tx.us/gis/raster.html
20 ft contour
100 ft contour
Stream Center Line
67 56 49 46 50
12 11 12
53 44 37 38 48
58 55 22 31 24
61 47 21 16 19
3453
50
30 m cell
cell
(cell value)
Cell Definition
Filling in the Pits
• DEM creation results in artificial pits in the landscape
• A pit is a set of one or more cells which has no downstream cells around it
• Unless these pits are filled they become sinks and isolate portions of the watershed
• Pit filling is first thing done with a DEM
+ =
Take a mapped stream network and a DEM Make a grid of the streams Raise the off-stream DEM cells by an arbitrary elevation increment Produces "burned in" DEM streams = mapped streams
“Burning In” the Streams - Improve accuracy based on photograph
67 56 49
53 44 37
58 55 22
1
67 56 49
53 44 37
58 55 22
1
26.162
4467=
−14
1
5367=
−Slope:
Direction of Steepest Descent
0 0 000
0
0
0
0
0
0
0
0
03 2 2
11 1
1 152 5
24 1
Flow Accumulation Grid
Grid Network Count the # of contributing cells
Watershed and Drainage Paths Delineated from 30m DEM
Automated method is more consistent than hand delineation