Descriptive Statistics. Project 3 CIVL 3103

Transcription

1 Project 3 CIVL 3103 Descriptive Statistics Introduction In our course, we have discussed interpolation for a single set of point data. However, many datasets that are used by engineers are spatial in nature, and require different types of analysis to account for the spatial variability. Interpolation is one analysis tool that can be applied across a spatial extent. For this project, you will learn to develop a surface interpolation from point data, which can then be used for a variety of analyses. Project Data Description For this project, you will need to download several available GIS files. The first is a dataset of traffic volume history available from the Tennessee Department of Transportation ( Choose ESRI shapefile from the download options at the bottom of the page. The second file you will need is the county boundary file for the state of Tennessee. You can access this here: and select the download icon next to the County Boundaries listing under Administrative Divisions. Project Requirements You will learn to create an interpolated surface from point data for this project, and to work with multiple surfaces identify changes. You will also learn to edit and clip shapefiles to facilitate your analyses in the examples presented below. 1. Return to ArcMap and open a new project file. Add the TDOT traffic history and the County Boundaries shapefiles to your project. 2. First we will select just the Shelby County boundary, and save it to a separate shapefile for use later. From the Selection drop down menu at the top of your project window, select Select by Attributes. Choose the tn_counties shapefile for the Layer field. Now we will set up our query to select just Shelby County. Double click on County in the box in the center of the popup window that displays the available fields from your shapefile. Next, click on the = symbol from the operation options. Then click the Get Unique Values button adjacent to the operation buttons to display all of the county names in your dataset. Double-click on Shelby. You should see an equation displayed in the box at the lower portion of the pop-up window that indicates your query operation. (See figure on next page for example). When you have the correct formula, choose Apply and then Ok to return to your data view. 3. Next, right click on the tn_counties name in the legend of your Data View in order to display the pop-up menu. Choose Data and Export Data from this menu. In the Export menu, choose Selected features and then select a location and name for the shapefile that will contain just the Shelby County

2 boundary. Click Ok to create the shapefile, and then select Yes to add it to your project. 4. Next, we will create a surface from the TDOT traffic history data. You will need to make sure the Spatial Analyst extension in ArcMap is turned on to have access to these tools. To check this, under the Customize menu, click on Extensions. Make sure the Spatial Analyst extension is checked. Then click on the Arc Toolbox button ( ) to display the menu of analysis options. (see figure on following page for example). 5. Click the + next to the Spatial Analyst Tools to display the options available through this extension. Under this menu, click the + next to Interpolation to display the tools available for interpolating surfaces. The tool we will use is called Kriging. Kriging is a geostatistical method used to interpolate a surface from a set of point data. It is a type of least-squares estimation, and many different functions can be used to establish the interpolated surface. To open the Kriging tool, double-click on the name or the hammer in the Arc Toolbox menu.

3 6. For the Input point features box, select the TDOT traffic history shapefile. For the Output surface raster box, select the location where you would like to save your surface file, as well as the name you would like to use. Under Z value field select ADT 2011 (ADT = average daily traffic). Use the default settings under semivariogram properties, but be aware that this is how you can change the type of functions used in the interpolation. Click Ok to create your surface. It will take a few minutes to produce the surface, and you will see it displayed behind your data when it is complete. You have now interpolated a surface that indicates how average traffic volumes vary across the county. Your surface files are referred to as raster files. 7. You can also conduct analyses between a set of raster files. For instance, to create a surface that estimates the change in ADT between years, you can do this using the Minus tool (located in the Spatial Analyst toolbox under Math), and using two surfaces generated for ADT (for example 2011 and 2006 surfaces). You can change the symbology (colors) used in the newly created raster image by double clicking on the legend in the Table of Contents in your Data View and selecting an alternate color ramp. 8. Finally, you can clip out just the portion of the data in your raster files that is within Shelby County. To do this, use the Shelby County boundary as a cookie cutter for the raster files. Under the Data Management heading in

4 Arc Toolbox, select Raster then Raster Processing and then the Clip tool. You will select the raster that you would like to clip, provide the Shelby County boundary shapefile as the boundary that you would like to use to clip the raster, and then specify where you would like to save the clipped shape.

5 (figure above shows example of clipped raster image.) Now, using what you have learned from the exercise above, answer the following questions. You should provide a set of maps to support your response. Be sure to include appropriate titles, axis labels, legends, and north arrow, etc., on your figures. You will need to change to the Layout View (look for this symbol at the lower lefthand side of your project window ) in order to have the legend, north arrow, scale options available in the Insert menu options. Your responses should be in a technical report format, using Times New Roman or Arial font, size 10 or 12, with double spaced text. 1. In previous projects, you have been asked to suggest high priority transit corridors/areas of the county to MATA as they review their current routes and plan for the future based on analysis of data available from the Census Bureau. Now, you will look at trends in traffic volumes to determine what recommendations you can make to MATA based on the traffic growth over the past 10 years. Create a surface from the 2011 ADT and the 2001 ADT values, and then subtract these surfaces to create a representation of the traffic growth over the past 10 years. Use this surface, along with other data (You may use the road shapefile from Project 1, or add an aerial image to help you determine possible causes for the changes you are seeing if you like.

6 You can access the aerial files by clicking on the arrow next to the Add Data button and selecting Add basemap.) to justify your recommendations. Grading Rubric Requirement Formatting Requirements Title Page Use proper grammar Appropriate font and spacing All figures have titles, legends, scale, north arrow (if appropriate) Technical Requirements Introduction to the problem/question you are addressing Text clearly identifies the data used, how the traffic volume trends were obtained, and why this information is pertinent to MATA s decisionmaking process Graphics presented clearly support analysis and recommendations outlined in the text Text refers to each figure and explains what is presented Conclusion section summarizes recommendations Point Value 10 pts pts. 10 pts.