Maps by Computer – Part 2

1. Maps by Computer – Part 2 GEOG 3530/8535 University of Nebraska at Omaha

2. Slivers

3. Digitizer x coordinate y coordinate Accuracy: 0.001” Repeatability: 0.003” Impossible to hold hand steady at that degree of resolution.

6. Arc/Node Topology Arc Begin Node End Node Right Poly Left Poly 1 I II A 0 2 II III B 0 3 III IV C 0 4 V I B 0 5 III V B C 6 IV V D C 7 I IV D A 8 II IV A B

7. Slivers make polygons Simple Polygon Arc/node Polygon Expected 200 polygons After conversion, we had over 10,000 polygons Solution: Deleted smallest polygons and merged with surrounding polygon. Conversion

8. Merging Polygons

9. Redistricting – electoral, congressional

11. Coordinate Transformations 2x transformation 2,2 becomes 4,4 4,4 becomes 8,8

13. Rotation u = cos (radang) v = sin (radang) for i = 1, n tempx = x(i) * u + y(i) * v y(i) = -x(i) * v + y(i) * u x(i) = tempx next i

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

15. Object Graphics - Illustrator

17. Coordinates

18. Raster Overlay How many commercial/100 year flood pixels?

19. Overlay