Exercise 6 Coordinate Systems and Map Projections The following steps describe the general process that you will follow to complete the exercise. Specific steps will be provided later in the step-by-step instructions component of the exercise. Start ArcMap and add the county boundary data to the data frame. Change the data frame coordinate system to UTM Zone 16 to better depict the actual shape of Indiana. Add the Interstates data as a new layer in the data frame. Remove the interstates data from the data frame. Open ArcToolbox and assign the coordinate system information to the interstates shapefile. Return to ArcMap and add the interstates data to the data frame. Add the GNIS data to the data frame and then create an X, Y layer from that table. Save your work to a new map document named EX6 in the assigned folder on your desktop. Exit ArcMap or, time permitting, continue to the challenge exercise. Step-by-Step Instructions Task 1: Start ArcMap and add the county boundary data from your downloaded dataset to the data frame. Start ArcMap. The ArcMap startup window will appear. Click New Maps on the left. Make sure the Blank Map icon is selected and then click the OK button. If you are not prompted to start a new empty map, simply proceed to the next step.
Click the Add Data button to open the Add Data window Navigate to your EX6 folder and double-click the BndryGDB.mdb data source to view the list of available feature classes in the geodatabase. A geodatabase is a relational database that stores spatially referenced data. Geodatabases store feature classes which, like shapefiles, contain a single type of geometry. In this example, the BndryGDB geodatabase contains a single polygon feature class named hzcounty. Click the hzcounty feature class and then click the Add button to add this data as a new layer in the Table of Contents and to close the Add Data window.
Task 2: Adjust the data frame coordinate system to better depict the shape of Indiana. Right-click the Layers data frame and choose Properties from the Data Frame context menu to open the Data Frame Properties window. The Hazus-MH data provided to users are stored in the North American Datum 1983 geographic coordinate system. As is the case with many national databases, this coordinate system was selected for the entire Hazus-MH dataset to provide nationwide consistency. Unfortunately, geographic coordinate systems tend to produce maps that are distorted in appearance. ArcGIS allows you to address this issue by reprojecting a data frame and all the layers in it to a different coordinate system on the fly. This means layers can be visually presented in a coordinate system other than that in which they actually are stored. Click the Coordinate System tab in the Data Frame Properties window. If not already open, click the Plus (+) to the left of the Projected Coordinate System folder in the upper section of the Data Frame Properties window and navigate down to the Projected Coordinate System>UTM>NAD 1983 folder. Choose NAD 1983 UTM Zone 16N.
Click the OK button at the bottom of the Data Frame Properties window to change the data frame s coordinate system to UTM Zone 16. Your map view window may appear blank because of the new yay the counties of Indiana are projected. If this is the case, click the Full Extent button in the navigation bar at the top of the ArcGIS window to see the counties again. The map of the counties of Indiana has been relocated to the center of the data frame window. Also note the change in the shape of Indiana as a result of changing the data frame coordinate system. Task 3: Add the interstates shapefile as a new layer in the data frame. Click the Add Data button to open the Add Data window. Navigate to the EX6 folder and choose the shapefile named Interstates_IN.shp. Click the Add button in the Add Data window to add the layer. Task 4: Remove the interstates layer from the data frame. Right-click the Interstates_IN layer and choose Remove from the layer context menu to remove that layer from the data frame. Reminder: When you remove a layer from a data frame, you are simply breaking the link between the map document in which you are working and the data source. You are not actually deleting the data. Task 5: Open ArcToolbox and assign the coordinate system information to the interstates shapefile.
Open ArcToolbox by clicking the ArcToolbox symbol in the Standard Toolbar. Navigate to the Data Management Tools>Projections and Transformations and double-click the Define Projection Tool. The Define Projection window should appear as shown below.
Click the Browse Feature Class window. button in the Define Projection window to open the Input Dataset or Navigate to the EX6 folder and choose the data source named Interstates_IN.shp. Click Add to close the Add data window. The data source will appear in the Define Projection Tool window. The Coordinate System is presently defined as Unknown.
Click the Select Coordinate System window. button to display the Spatial Reference Properties The Spatial Reference Properties window allows you to obtain or define coordinate system information in a variety of ways. You may select a coordinate system from a predefined list of the major coordinate system options. This included geographic coordinate systems as well as projected coordinate systems. You may obtain projection information from another data source for which this information has been defined already. Many organizations will create a master projection file that is used as the reference for all other files. You may define your own customized projection. This option is not recommended unless you thoroughly understand map projections because you can significantly and possibly adversely impact the quality of your data and all decisions that are based upon the data.
Navigate to Projected Coordinate Systems > UTM > NAD1983 UTM Zone 16N.prj. Click the OK button to close the Spatial Reference Properties window and to update the Define Projection window. Click OK to close the Define Projection window. The Define Projection Tool will create the projection file in the same folder and with the same name as your source data. This file has a prj extension. However, because of the way ArcGIS combines files into the GDB and MDB files, it will not appear in your Catalog files. Close ArcToolBox by clicking the X in the upper right corner of the ArcToolbox window. Interstates_IN data have now been added to the map.
Although the roads appear similar to what they did before defining the coordinate system of the data, you now can have confidence that ArcMap is displaying the data correctly. Many types of point data are stored in a text file format or some other database format; doing so typically saves disk space. In addition, data acquired from a global positioning satellite (GPS) receiver often can be downloaded into a GIS system as X, Y data. The next section of the exercise explains the process for viewing these types of data sources in ArcMap. Task 7: Add the IN_DECI.dbf, whics is a dbase table containing X and Y coordinates for cities and towns in Indiana, to the data frame. Then create an X, Y Layer from that table. Click the Add Data button and navigate to the EX6 folder. Select IN_DECI.dbf and click the Add button. The IN_DECI data source should appear in the Table of Contents.
Right-click the IN_DECI.dbf table in the Table of Contents and choose Open from the context menu to open the table. There are fields in this table that contain X and Y coordinates for each record. These fields are lamed LAT2 for latitude and LON2 for longitude. These fields contain the coordinate information for each city in the format required by ArcGIS. The presence of this information in the table is what makes it possible to display the table records as point features. When you are finished reviewing the contents of the Attributes of IN_DECI.dbf table, click the X in the upper right corner of the table window to close the table. Right click on the IN_DECI.dbf table in the Table of Contents and choose Display XY Data to open the Display XY Data dialog box.
For table containing XY fields, you need to specify the coordinate system in which the coordinates are stored. To do this: Click the Edit button. Navigate to Geographic Coordinate System > North America > North American Datum 1983. When you have selected the coordinate system, click the OK button to close the Spatial Reference Properties window.
Click OK to close the Display XY data window. The map should appear as shown below.
Save your work to a new map document names EX6.MXD in the EX6 folder. Challenge Exercise Time permitting, complete one or both of the following additional tasks. Task 1: Explore the GNIS Data The Indiana file IN_DECI.dbf contains more than 3,400 points representing the locations of populated places in Indiana. This type of data is available for the entire United States. To see the variety of information available in this data source, create a thematic map based on the POP field using the graduated color option. Change the thematic map you just created to show elevation based on the features in the GNIS file. Use the Graduated Color option based on the ELEV field. Task 2: Explore Additional Web Resources Many free data resources are available from the Internet. Unfortunately, many of these resources do not include projection data. Search the following websites for additional free data resources that contain spatial data located in the State of Indiana. National Atlas www.nationalatlas.gov Indiana Map www.indianamap.org Locate the metadata on these websites and identify the coordinate system in which the data are stored. Download one or more data files from these sites and use the ArcToolBox Define Projection Wizard to assign the appropriate coordinate system to the data. View the data in ArcMap. Task 3: Explore the Project Wizard As you have seen in this exercise, it is possible to use the ArcMap on-the-fly projection ability to visualize data in any map projection, regardless of the coordinate system in which the data actually are stored. However, as discussed in the lecture, it is important to physically alter the coordinate system that a file is stored in so you can accurately complete tasks such as editing or advanced spatial analysis.
Try using the ArcToolBox Project Wizard (accessed by opening ArcToolbox and navigating to Projections and Transformations > Feature > Project) to change the map projection of the Interstates_IN shapefile from NAD_1983_UTM_Zone_16N to NAD_1983_StatePlane_Indiand_East_FIPS_1301_Feet. Save the projected file in the EX6 folder to a new shapefile named Interstates_IN_Stateplane. Reminder: The way that the Project Wizard works is almost exactly like the way the Define Projection Wizard works. You create a new file in a new map projection as part of the process of using the Project Wizard; you merely document the coordinate system of an existing file when you use the Define Projection Wizard. Summary In this exercise, you began to explore some of the issues and challenges presented when working with spatial data. Projected data can be used for many purposes. By understanding how your data are projected and how to go about defining or changing the projection, you can complete accurate calculations and/or create maps with a visual style that suits your project needs.