Exercise 3 Overview Slope calculations by hand Verifying

Exercise 3 Overview • Slope calculations by hand • Verifying using Arc. GIS • Automating and applying to larger dataset using Modelbuilder • Spatial Analysis of San Marcos Elevation and Precipitation • • • Projecting rasters Examining and visualizing topography Zonal average calculations Thiessen polygons Surface smoothing to average precipitation

Slope and Aspect https: //pro. arcgis. com/en/pro-app/tool-reference/spatial-analyst/how-slope-works. htm

Arc. GIS “Slope” tool y a b c d e f g h i x 1 2 1 a y b d c e g f h i x

Arc. GIS Aspect – the steepest downslope direction Use atan 2 to resolve ambiguity in atan direction https: //pro. arcgis. com/en/pro-app/tool-reference/spatial-analyst/how-aspect-works. htm

Example 30 a d g 80 69 60 b e h 74 67 52 c 63 f 145. 2 o 56 i 48

Hydrologic Slope (Flow Direction Tool) - Direction of Steepest Descent 30 Slope: 30 80 74 63 69 67 56 60 52 48

Eight Direction Pour Point Model 32 64 16 8 128 1 4 2 ESRI Direction encoding

The D Algorithm z 0 z 2 Elevations at each vertex zi z 1 If 1 does not fit within the triangle the angle is chosen along the steepest edge or diagonal resulting in a slope and direction equivalent to D 8

D∞ Example 30 80 74 eo 69 67 e 7 60 52 284. 9 o 63 56 e 8 48 14. 9 o From Arc. GIS Pro Help:

10 4 z 5 z 0 3 5 26. 0 26. 4 6 z 6 25. 8 7 2 1 8

Subwatershed Precipitation by Thiessen Polygons P 2 P 1 A 2 A 3 P 3 • Thiessen Polygons • Intersect with Subwatersheds • Evaluate A*P Product • Summarize by subwatershed

Subwatershed Precipitation by Thiessen Polygons • Intersect with Subwatersheds • Evaluate A*P Product • Summarize by subwatershed