Lab 6: Terrain Analysis & Spatial Modeling
Introduction
This lab introduces using ArcGIS ModelBuilder as a tool to design and build spatial models.
Instructions
Based on the assigned readings for this week, answer questions in Part I of this lab. Then proceed to the next Parts and complete the hands-on exercises. Before working with the lab data, copy it from the course website onto your flash drive.
Deliverables
Answer the questions marked in bold and produce the required outputs. Your lab document should be typed, well organized, and submitted according to the course “How To” guidelines.
PART I: Assigned Readings
Textbook – Bolstad, Chapter 13
- What do we mean when we say that most cartographic models are temporarily static?
- How is a “flowchart” related to a cartographic model?
- When defining criterion layers within a cartographic model, when might you use a “discrete ranking” vs. a “continuous ranking”?
- How do spatial-temporal models differ from cartographic models?
Textbook – Bolstad, Chapter 14
- Why are standards so important in spatial data?
- What are the differences between “accuracy” and “precision”?
- What is the NSSDA, and how does it help us to measure positional accuracy?
- How are errors in nominal attribute data often reported?
ESRI ArcGIS 10 Online Help Files
- What are the three main types of model elements?
- How do you add data and tools to Model Builder?
PART II. Terrain Analysis Project
Project Description
Elevation data, also known as terrain data, are important for many kinds of analysis and are available in many forms, from many sources and resolutions. In the U.S. there have long been available nearly nationwide Digital Elevation Model (DEM) data at 30-meter resolution. Since the early 2000’s these have largely been replaced by 10-meter resolution DEMs, and now many parts of the country are developing higher resolution DEMs, and 1 to 3 meters, based on LiDAR data collections.
The goal of this project is to get a better understanding of the terrain in this region for possible building construction on site. To do this, you will look at a 3m DEM from 2006, create an elevation profile, and understand the viewshed from the proposed construction point.
Preparing for Analysis
Step 1. Coordinate Systems/Projections
Check to see what coordinate system your datasets are in. If they are different, convert the vector shapefile (viewspot) to the same coordinate system as the raster. Make sure that your Data frame is set to the same PCS.
Step 2. Setting your Geoprocessing Environments
- Set a current workspace
- Set the output coordinate system to ‘Same as Display’
- Set the Cell Size to the driftless DEM
- Set the default to Build Pyramids using the Bilinear or Cubic resampling technique
- Set any other environments you think are necessary
Step 3. Sketch your Workflow
Read through the Terrain Analysis project and create a sketch workflow.
Analysis
- Start ArcMap and create a new blank map. Add the raster driftlessto your map view, and inspect it. Use the Layer Properties > Source tab, and the Identify tool.
- What is the cell resolution for the driftless layer? What are the highest and lowest elevation values?
- What are digital elevation models (DEMs), and why are they used so often in spatial analyses?
- Derive the hillshade for driftlessusing ArcToolbox > Spatial Analyst Tools > Surface Analysis > Hillshade.
- Keep the default of “315” for the Azimuth, specify “25” for the Altitude, and model shadows. Name the output file hs_drift.
- Position the driftless layer so that it draws over the hs_drift layer in the TOC.
- Apply a multi-color ramp (e.g. blue-green-yellow-red-brown-white) to the driftless layer (Layer Properties > Symbology), and make it semi-transparent (Layer Properties > Display, set the transparency to something like 50%). You should get a display similar to the one below.
- If 3D Analyst extension is NOT already turned on, go to Customize > Extensions, and check 3D Analyst.
- Next, turn on the toolbar - Customize > Toolbars > 3D Analyst.
- This displays a new set of tools, including the icons below.
- We’ll now explore the Line of Site and Profile View options.
- First, add the viewspot shapefile to your map. This shapefile displays a single point, in the bottom left portion of the driftless DEM. If you have trouble seeing it, you can change the symbology to make it more visible. This represents the area where a proposed building will be constructed.
- Activate the Line of Site tool. on the 3D Analyst toolbar. This will open a Line Of Site window. Enter “2” for the Observer offset value (height, in meters here), and leave a value of zero “0” for the Target offset. Close the Line Of Site window.
**Observer Offset is the eye level of the observer used to determine what is visible from the observer's location. An observer with a height of 0 will have a more obstructed view than an observer with a height value indicated
Target Offset is the height of the target point above the surface. A target with a height of 0 will be less visible than a target with a given height greater than 1**
- Now, left-click approximately on the point in the viewspot shapefile, found in the southwest quadrant of the driftless DEM. Move the cursor up to somewhere near the top of the DEM, and left-click again. If you make a mistake push Delete and start over. This line of sight is a proposed area for building a road and you will want to get a clear idea of the change in elevation along this proposed route.
- This should display a Profile Line over the DEM, similar to the one shown to the right.
- The profile line is a graphic element placed on the data and layout views. The default settings show areas not visible along the line colored in red, and visible areas colored in green.
- While the profile line is selected, left-click on the Profile Graph tool (as shown below) to display the corresponding Profile Graph.
- The profile graph shows the same profile line trajectory, but in a side view, and uses the same green/red coloring scheme. It shows the elevations on the vertical axis, and the horizontal distance on the horizontal axis.
- Note that right-clicking on the profile graph displays a drop-down menu, and using the Properties option (see below right) allows you to change some of the graph properties, e.g. titles.
- Add a graphic of the plot to your layout by right-clicking on the profile graph and selecting Add to Layout, or you may Export to one of several image formats.
- Double-check to see that it has appeared in the layout view.
While the Profile tool and graph show visibility along a specific path (road), we also want to know all areas visible from a point, rather than just along a profile line. What view will be visible from the proposed building site? We can create a data layer showing areas that are visible vs. hidden, using the Viewshed function.
- To access this function, go to ArcToolbox > Spatial Analyst Tools > Surface > Viewshed.
- Specify driftless as the input raster, viewspot as the input point feature, and name the output raster viewshed, and a Z factor of 1.
- This will create an output raster with all cells within the area covered by driftless categorized as either “visible” or “not visible” from the viewspot point.
- Make the non-visible cells transparent (i.e. assign no color to the symbols), and assign your choice of color to the visible cells. Switch to Layout view, and make a map that includes the driftless visual (hillshade & DEM with specified color scheme), the elevation profile for your line of sight, and the viewshed analysis results. Add the usual layout elements to create a presentation quality map. Save your map project.
- Export your map and insert into your lab document.
- Insert in your workflow for the Terrain Analysis project.
PART III: Building a Spatial Model using ArcGIS ModelBuilder
ArcGIS ModelBuilder is an application that allows you to visually build workflows. In this part of the lab, you will gain experience building spatial models in Model Builder, using models for workflows using Spatial Analyst tools, and create a model using a workflow from a previous lab.
Copies of the tutorial data can be found on the classroom (HT301) computers on the T:Thawspace drive. You may have also downloaded the data when installing the software on your home computer (in a folder called ArcTutor).
- Model Builder Tutorial
- In order to get some practice working with ModelBuilder, complete twotutorials forArcGIS Desktop 10.1
(
- Scroll down to find “ModelBuilder – Executing Tools” and “ModelBuilder – Creating Tools” tutorials.
- Complete the Executing Tools tutorial (Steps 1-7) and include a screenshot of your model.
- Complete the Creating Tools tutorial (Steps 1-12) and include a screenshot of the final model you create, as well as the final output of the model in ArcMap.
- Spatial Analyst Tutorial
- Open ArcGIS Desktop 10.1Spatial Analyst tutorial (
- Read through the “About the ArcGIS Spatial Analyst Tutorial” section
- Complete Exercises #1-3
- At the end of the Spatial Analyst Tutorial Exercise #3, submit the following items:
- Export your model to a graphic/image and include in your lab document.
- Take a screen shot of your ArcMap Map View, showing the polygon feature for the optimal new school site. Include the screen shot as an image (JPEG, GIF or PNG) in your lab document.
- North Portland Light Rail Stations Model
- In Lab 4, Part IV, you looked at accessibility of North Portland Light Rail Stations. You will use this scenario to create a spatial model using ArcGIS Modelbuilder.
- Create a spatial model for Lab 3, Part IV (Accessibility to North Portland Light Rail Stations) – from the start of Part IV through the use of the “Clip” tool.
- Export your model to a graphic/image and include in your lab document.
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