Lab 1: Raster Modeling in ArcGIS

Introduction

This lab teaches you how to do raster spatial analysis and introduces map algebra.  Download the sample file (Spatial.zip) to your network drive and unzip it there. If unsure, ask the TA how to map your network drive or visit this webpage.

Instructions

 

Part I: Introduction to ArcGIS Spatial Analyst
You will use the Acrobat book called Using ArcGIS Spatial Analyst (Using_Spatial_Analyst.pdf) to do the exercise. The pdf file can be found in the I:\Students\data\GIS\ArcGIS9.1_documentation\ESRI_Library\ArcGIS_Extensions folder. Read Chapter 1 and do the Quickstart Tutorial exercises in Chapter 2. Answer the following questions and produce the following outputs.  Return them to the TA by the due date.  Labs should be typed, include your name, be well organized, and be stapled together.

  1. There are many different choices for defining the analysis extent in Spatial Analyst.  Explain the analysis extent and describe the options that you may use in ArcGIS to select the extent.
  2. Explain the different options available in ArcGIS to select a cell size for analysis outputs.
  3. What does the value field represent in the ArcGIS raster format? (Hint: The two main types of data are represented differently with the value field)
  4. How do you reclassify nominal data such as landuse?
  5. What is cost weighted distance as opposed to Euclidean distance?
  6. Calculating the shortest cost path requires a cost distance raster layer, a cost direction raster layer (which defines the direction of the lowest cost), and a destination file.  This type of calculation is called the least cost pathway.  What does the resulting map really mean?  The least cost of what?
  7. At the end of Exercise 3 of the tutorial, export the final map to a JPG and paste it into your lab MS Word document.

 

Part II: Understanding Raster Analysis in ArcGIS
Skim Chapters 4, 5, and 6 and answer the following questions.

  1. What is a region?
  2. Explain the concept of NoData.
  3. Before specifying a cell size you should take into account, the resolution of the input data, the desired response time, and the application and analysis to be performed.  Explain each by giving an example.
  4. How do you assign attributes to a raster data set for categorical data and how does it differ with assigning attributes to continuous data sets?
  5. Spatial analyst can use either features or grids as inputs.  When a feature is used the software first rasterizes the feature and then performs the operation.  Give examples of spatial analyst operations using both types of input (raster and vector).
  6. When creating rasters from existing maps you must consider age, accuracy, resolution, and compatibility.  Explain each of these concepts.
  7. Explain the difference between local, focal, zonal, global, and application functions.

 

Part III: Spatial Analysis in ArcGIS
Read Chapter 7, do the following tasks, and answer the following questions.   Log onto the Oregon Geospatial Enterprise Office web site and click on ‘Oregon Geospatial Data Clearinghouse’. There are six columns in the table. The E00 file is an ArcInfo interchange file (also called an ArcInfo Export file).  ShapeFile is an ArcView shapefile.  Image is a preview image.  Metadata is descriptive information about the data.  Not all data are available in both Shapefile and E00 formats. Click on the E00 file for County Boundaries-Oregon (blm) file size.  Save it to disk in a location that you have access to.  Navigate to the file using Window's Explorer.  Double click on the zip file to unzip (extract) its contents.  Then download and unzip the following E00 files: Cities (USGS), Highways (USGS), Population (USGS), State Boundary (USGS), and Vegetation/Species(Idaho F&W GAP vegetation, 1:250,000).  After you unzip them all then you can convert the E00 files into ArcInfo coverages.   To avoid confusion, it’s best to save these coverages in a new folder, separate from the files that you unzipped.   Open ArcToolbox, choose >Coverage Tools >Conversion >To Coverage >Import from Interchange file and then choose the first E00 file and an output name and location for the coverage.  Import each of the other files into ArcInfo coverages in the same way.

Start ArcMap and open a new empty view.  Click the -ADD Data- button and add all of the ArcInfo coverages to your map by double-clicking on them individually and choosing a feature class.  For each coverage, you will specify the feature class that you want to add to the map (coverages and geodatabases may have multiple feature classes while shape files only have one type of feature per data set).  The feature classes used by this exercise are: Highways - arc, State Boundary - polygon, Counties - polygon, Population - point, Vegetation/Species - polygon, Cities - point. Once all of the coverages are added to the map, right-click on the data frame properties at the top of the table of contents (named 'layers').   Click on the general tab and choose feet for the map and display units. If these fields are grayed out, then first set the linear unit to foot under the coordinate system tab and modify button, then set the units under the general tab.  

The projection information was imported with the coverage.    If you would have brought in a ShapeFile then you would have had to put this information in manually. The projection parameters are as follows:

Projection: Lambert Conformal Conic
Datum NAD83
False_Easting: 1312336.0
False_Northing: 0.0
Central_Meridian: -120.5
Standard_Parallel_1: 43.0
Standard_Parallel_2: 45.5
Scale Factor: 1.0
Latitude_Of_Origin: 41.75

Now set the Spatial Analysis options as follows:
Working directory: to one you have write access
Analysis Extent: use the Oregon State Outline file
Cell Size: 5000

You will now do several spatial analyses using the Spatial Analyst menu commands. Make sure that the maps that you create have the SA# as part of their title.

SA #1: Calculating Distance from Highways using the Euclidean Distance Tool

Under the Spatial Analyst toolbar choose Distance, Straight Line and use the highway coverage as the Distance to file.
Make a map of the result, add your name using a text box, and print it.

SA #2: Allocating Space using the Allocation Tool

Under the Spatial Analyst toolbar choose Distance, Allocation and use Cities as the Assign to coverage.
Make a map of the result and print it with your name.  Using a text box describe the map in your own words directly on the map.

SA #3: Calculating Population Density using Density Functions
Under the Spatial Analyst toolbar choose Density, Density Type-simple, Search Radius-100,000, Population Field-pop85.
Make a map of the result and print it with your name.  Using a text box describe what the units mean, directly on the map.

SA #4: Highway Accessibility by County Using Zonal Statistics
Under the Spatial Analyst toolbar choose Zonal Statistics, Zone Dataset-county coverage, Zone Field-name, Chart Statistics-checked, Join Output Table to Zone Layer-checked, Value Raster-use the result of SA#1 (Euclidean Distance Surface From Highways)..
Then make a choropleth map using the Oregon County vector coverage by using the zone mean statistic as the attribute.  Using a text box describe what the units mean, directly on the map.

SA #5: Rasterize a Vector File and Use it To Calculate Vegetation Diversity Using a Neighborhood Statistic
Under the Spatial Analyst toolbar choose Convert, Features to Raster, Input Features-Vegetation, Field- com_code.   Under the Spatial Analyst toolbar choose Neighborhood Statistics, Input Data- state vegetation raster, Field- value, Statistic Type- variety, Neighborhood-rectangle (3x3).  Then make a map of the result.  Using a text box, describe what the units mean and why they have the range they do.

SA #6: Reclassify the Raster Vegetation Variety Neighborhood Surface into Two Classes
Under the Spatial Analyst toolbar choose Reclassify, Input raster- variety surface created in SA#5, Reclass Field- value, Method- equal interval, Classes-2.  Then make a map of the result.  

SA #7: Using the Raster Calculator to Change Cell Values (to m from feet), the Reclassification Tool to Reduce the Number of Classes, and Vectorization
Under the Spatial Analyst toolbar choose Raster Calculator, double click on the distance to highways raster created in SA#1, click on /, type 3.28, and click Evalutate.  Then reclassify the result into 3 natural breaks classes.  Then convert the raster to a vector by choosing Convert, Raster to Features from the Spatial Analyst menu (it doesn’t matter which field you use for this operation).   Then make a map of the result that includes a legend.

 

Part IV: Implementing Map Algebra Commands Within the Raster Calculator
First review Appendix A of the tutorial book.  The Spatial Analyst Raster Calculator allows you to use all ArcInfo MapAlgebra GRID commands and functions.  Learning map algebra is like learning any language.  Once you know the syntax then you need to increase your vocabulary.  In this exercise you will implement one map algebra function using the Raster Calculator.   First rasterize the highway vector coverage that you downloaded in Part III and call it HW.  Then choose “Programs -> ArcGIS -> ArcInfo Workstation -> ArcDoc” and select “Contents -> Command Reference for ArcInfo Extensions -> GRID -> Alphabetical List of Grid Functions.”  This is a comprehensive help system for ArcInfo MapAlgebra.  Read the help topic for Thin.  Then open the raster calculator and type: thin([HW]) and then click evaluate.  If it works then you have implemented your first MapAlgebra command that is not available through buttons or menu commands within Spatial Analyst.  Make a map of the result and include a description of the result in a text box as well as your name.