Lecture 18: Spatial Analysis Using Rasters Jeffery S. Horsburgh CEE 5190/6190 Geographic Information Systems for Civil Engineers Spring 2016

Reminders Assignment 6 posted in Canvas today

Objectives Become proficient in the use of GIS tools to conduct spatial analyses Work with data in formats common to GIS, including shapefiles, rasters, and geodatabases Apply spatial analysis routines for problems relevant to Civil and Environmental Engineering using vector and raster data

Raster Analysis for Change Detection How is land cover changing in Cache County, UT? ◦What is the total new urban area that has been created? ◦What type(s) of urban area have been created, and how much of each type? ◦Which land cover class lost the greatest area? How much? ◦Which land cover class gained the greatest area? How much?

The Setup Download NLCD 2001, 2006, and 2011 data from MRLC Create new geodatabase Project NLCD rasters to NAD 1983 UTM Zone 12N, writing output to geodatabase Extract Cache County boundary from AGRC’s counties shapefile Import county boundary to geodatabase

Analysis Objective Create a new, output raster where the classes include the unique combinations of land cover change (e.g., LC2001 versus LC2011) Use the output to assess where and how land cover has changed For now, we will ignore the 2006 data Number of Grid CellsWhat they were in 2001What they changed to by 2011 Most of them will not have changed

Step 1: Convert County Boundary to Raster Mask This will help us limit our analysis to Cache County Procedure: 1.Set raster geoprocessing environmental variables to ensure concurrent rasters – origin, extent, grid cell size, 2.Convert county polygon to raster mask 3.Result: Raster with value of 1 inside county – NoData outside county

Set Environment Variables ArcMap  Geoprocessing Menu  Environments Under Processing Extent ◦Set the extent to NLCD_2011 ◦Set the snap raster to NLCD_2011 This will ensure that we create a new mask raster that is concurrent with the input land cover rasters

Set Environment Variables Under Raster Analysis ◦Set Cell Size to “Same as layer NLCD_2011” We can’t set the mask yet because we still need to create it

Convert County Polygon to Raster Mask ArcToolbox Polygon- to-Raster tool System Toolboxes  Conversion Tools  To Raster  Polygon to Raster Make sure grid cell size = 30 m Name output “mask” and make sure it gets written to the Lecture18 geodatabase

Raster Mask Result

Set Mask in Environment Variables Under Raster Analysis Set Mask to your “mask” raster that you just created and that is in your data frame All subsequent raster operations will use the Environment Settings -Origin -Extent (rows and columns) -Cell Size -Mask

Step 2: Compare LC Rasters (2001 vs. 2011) Strategy 1.Identify places (grid cells) where there as been a change (2001 != 2011) 2.Attribute those changed grid cells with their value in 2001 AND their value in Calculate total areas of change based on the output raster attribute table

ArcGIS Raster Calculator

Step 2: Calculate Change Raster Use Raster Calculator System Toolboxes  Spatial Analyst Tools  Map Algebra  Raster Calculator Calculate a new raster where: “NLCD_2001” != “NLCD_2011” Call the output raster: “change_01_11” Save to your geodatabase

Change Raster Result 0 = No change 1 = Change

Step 3: Identify LC Class for Changed Area in 2001 Use Raster Calculator Calculate a new raster where: “change_01_11” * “NLCD_2001” Call the output raster: “change_01” Save to your geodatabase

Step 4: Identify LC Class for Changed Area in 2011 Use Raster Calculator Calculate a new raster where: “change_01_11” * “NLCD_2011” Call the output raster: “change_11” Save to your geodatabase

Step 5: Combine 2001 and 2011 LC Classes for Changed Area into One Raster Use ArcToolbox Combine tool

Step 5: Combine 2001 and 2011 LC Classes for Changed Area into One Raster System Toolboxes  Spatial Analyst Tools  Local  Combine Calculate a new raster that combines “change_01” and “change_11” This is essentially a boolean “AND” expression Call the output raster: “LC_Change_01_11” Save in your geodatabase

Result All unique combinations of land cover in 2001 versus 2011 and the count of grid cells in each category

For convenience, add an “Area_m2” field to the table

Back to our questions… How is land cover changing in Cache County, UT? ◦What is the total new urban area that has been created? ◦What type(s) of urban area have been created, and how much of each type? ◦Which land cover class lost the greatest area? How much? ◦Which land cover class gained the greatest area? How much?

What is the total new urban area that has been created? Query the result raster attribute table and sum area

What type(s) of urban area have been created, and how much of each type? Use “Summarize” function to create a summary table Right click on table column with categories Summarize Area_m2 by “Sum”

Summary Raster datasets facilitate simplified change analysis Geoprocessing Environment Settings help you constrain your analyses – and help ensure rasters are concurrent A raster mask can help you limit analysis to a specific geospatial area Raster calculator makes map algebra simple – you can build powerful expressions to compare datasets Raster attribute tables can help you summarize results

Assignment 6 Perform a land cover change analysis using the NLCD 2001 and 2011 data for Weber County, UT Calculate total area of land cover change from 2001 to 2011 Determine which land cover class lost/gained the greatest area Determine how much urban area was lost and created