Triangulated Irregular Network
Ann Arbor, Michigan
City of Ann Arbor contour map, with contours at a
five foot interval, is used to create a triangulated irregular network
in ArcView GIS, 3.2, Spatial Analyst Extension. Steep slopes can
be readily visualized and creeks and swales become evident. When
this sort of spatial analytic tool is used in conjunction with other existing
maps, guidelines for policy of where to develop and not to develop may
emerge. Base maps from City of Ann Arbor (thanks to Merle Johnson).
Legend is measured in feet above mean sea level. The interval in
the legend is five feet. The TIN was calculated from the five foot
interval creating 45 separate layers in which to perform calculations.
The GIS software, in selecting a default color ramp, did not select 45
colors to show change in grade. It grouped the data into subgroups
of 15 to 20 feet by color. Thus, each individual color represents
15 or 20 feet of elevation, ranging from deep blue at 750+ feet to rust
color at 975 feet. In particular,
750 to 800 feet: deeper blue to lighter blue,
800 to 850 feet: deeper green to lighter green,
850 to 900 feet: blue-green to chartreuse,
900 to 950 feet: yellow to orange, respectively
over 950 feet, rust.
In the map below, the parcel map is overlain on the
TIN as are layers for parks (stippled green), for water (blue), for street
centerlines (green lines), and for dams (magenta). Allen Creek enters
the river just south of the dam (north is at the top of the map)
A closer look allows more of the TIN to show through.