Exercise 8: Raster Processing with Booleans and Loops

Goals and Objectives

The purpose of this exercise was to use a suite of loops to clip and project a directory of scanned USGS topographic sheets into a seamless raster using Python.  The study area was Kettle Moraine. 

Methods

In this exercise, four scanned USGS topographic sheets were manipulated using Python to create a raster.  While developing this script, comments were used to annotate each section of code.  The following steps were taken: 

• importing system modules
• importing Python modules: os, time, datetime, shutil, ArcGIS extensions
• creating variables
• creating spatial reference object using coordinate system of a tile index
• using IF statement to set up loop
• adding all files of specified criteria to raster list
• setting up processing loop for each raster
• formatting raster names
• projecting all rasters
• creating polygon of raster's topographic footprint
• merging tiles
• creating IF statement to set up a FOR IN loop
• creating search cursor
• clipping rasters
• merging rasters together
• debugging and running script
• creating map in ArcMap

Results

The final map and script are shown below.  

Figure 1: map displaying four merged USGS topo quads