Using custom types to represent elevation data
A common goal for digital mapmakers is to try to have the onscreen results retain the
look of a paper map while offering all of advantages of a GPS receiver. I’ve developed a
method for presenting elevation information using colored polygon layers instead of
topographic lines. Here’s a sample of what can be done with this technique:
Map with elevation layers using custom types rendered in MapSource
If you’ve studied the possibilities of using custom types, you know that there are 8 levels
of draw order specified in your TYP file. Here’s a portion of a [_draworder] section:
; Large urban area >200k
; Small urban area <200k
; Rural housing area
; Military base
; Parking lot
; Parking garage
; Shopping center
…(up to 0x54)
The lowest numbers are drawn first, A polygon with a drawOrder of 8 would be drawn
above all other polygons, but below all polylines and points.
My goal was to utilize some of the unused polygon types, repurposing them to show
elevation in my maps.
The first step is to determine is the range of elevation data we intend to show in our map. This
depends entirely upon the data that’s available to you. You may have topo layer information
every 100 meters up to 3000 meters (as shown in the sample map above), or you may have topo
layers from 100’ to 500’ at 25’ intervals. The key is to pick layers at evenly spaced intervals, for
example every 100’ or every 300’. For my sample map, I followed directions available at
http://home.cinci.rr.com/creek/garmin.htm, and downloaded elevation data for the Seattle area.
The area that I’m working with has layers starting at 100’ with intervals every 25’, up to 500’.
That’s a total of 16 discrete elevations. 8 representative samples from this data would start at
100’, taking every other layer up to 450’ for a total of 8 ov