1. Digital Topography FE 423 - Lecture 2a

2. From Last Week: Grid the roads and stands using various grid sizes. Overlay and comment. Grid the stands, roads, and landslides to match the DEM grids. Do they line up? Overlay the road lines on the road grid. Comment. Repeat with polygons.

3. Which of majority, centroid, or weighted are most similar to the others? Are they more similar on large or small grid cells?

4. SCHEDULE

5. OUTLINE Representing topography Converting topography to grid Digital topography sources

6. FIRST... Out onto the lawn! Bring your jacket (or not) Enjoy the view!...wish you were an oceanographer? How do we represent the topography?

7. DIGITAL TOPOGRAPHY points, arcs, polygons, grids We can survey point elevations We can make contours of equal elevation or make polygons of elevation range or a grid with elevation at each node

8. Digital Elevation Data vs. DEM we collect data at points all points between must be modeled hence, Digital Elevation MODEL

9. Modeling Digital Elevation Data Connect the dots TIN - triangular irregular network Spline - minimum curvature fit IDW- inverse distance weighting Approximate Trend - regression

10. Digital Elevation Data Sources Points you might survey your own Contour lines popular old tool requires ArcInfo TOPOGRID Raster DEM ASCII USGS

11. ASCII Raster GRIDs

12. Getting Topographic Data Importing Raster data Import Data Source... Importing ArcInfo exported files C:> IMPORT71.exe coverage.e00

13. Reading from ArcDoc Spatial modeling –Cell-based Modeling with GRID Surface functions CURVATURE LATTICEDEM TOPOGRID

14. Discussion Problems: Go to Harvey’s 10-meter DEM page http://duff.geology.washington.edu/data/raster/tenmeter/byquad/index.html Download, unzip, import, and display a quad that you are familiar with Create contours and a hillshade image Find on the web the HJ Andrews data we have been using, download, import, and display.

15. Practice Problem 1: Identify the elevation of the center of each square

16. Practice Problem 2: Draw 100 meter contour lines from these elevations