Maps by Computer – Part 2

GEOG 3530/8535 University of Nebraska at Omaha

Slivers

Accuracy: 0.001”Repeatability: 0.003”

Impossible to hold hand steady at that degree of resolution.

Digitizer

x coordinate y coordinate

Arc Begin Node End Node Right Poly Left Poly1 I II A 02 II III B 03 III IV C 04 V I B 05 III V B C6 IV V D C7 I IV D A8 II IV A B

Arc/Node Topology

Slivers make polygons

Simple Polygon Arc/node Polygon

ConversionExpected 200 polygons

After conversion, we had over 10,000 polygons

Solution: Deleted smallest polygons and merged with surrounding polygon.

Merging Polygons

Redistricting – electoral, congressional

Coordinate Transformations

2x transformation

2,2 becomes 4,4

4,4 becomes 8,8

Rotation

u = cos (radang)v = sin (radang)for i = 1, n

tempx = x(i) * u + y(i) * vy(i) = -x(i) * v + y(i) * ux(i) = tempx

next i

Interpolation

What does squaring the distances do?What would the value be if distances cubed?

Object Graphics - Illustrator

Coordinates

Raster Overlay

How many commercial/100 year flood pixels?

Overlay