GEOREFERENCING HISTORIC MAPS USING ARCGIS DESKTOP 10

Transcription

1 5/20/2011 BALL STATE UNIVERSITY LIBRARIES GIS RESEARCH AND MAP COLLECTION GEOREFERENCING HISTORIC MAPS USING ARCGIS DESKTOP 10

2 GEOREFERENCING HISTORIC MAPS USING ARCGIS DESKTOP 10 *This tutorial is appropriate for users who have at least a basic working knowledge of the ESRI ArcGIS Desktop 10 software. Georeferencing a raster dataset by definition means to define its location in terms of map projections or coordinate systems. In this tutorial we will be assigning spatial coordinates to a historical Sanborn Fire Insurance map from 1911 using current road centerlines and aerial photography. Adding the Data and Turning on the Georeferencing Toolbar 1. Click on the Georeferencing Historic Maps Tutorial Data link from the GRMC tutorial page and download to your computer. 2. Unzip the contents of the folder to a location on your computer or external data device. 3. Open a new blank ArcMap document and add street_centerlines.shp from the Georeferencing Tutorial Data folder. You may have to Connect to the folder where you installed the tutorial data. 4. You will want to turn on the street_centerlines.shp labels for reference later. 5. Add the 2010_aerial.tiff raster file from the Georeferencing Tutorial Data folder. 6. In the Main Menu, Go To Customize>Toolbars>and Turn on Georeferencing Toolbar. The toolbar functions are shown in the graphic provided by ESRI below. Ball State University Libraries GIS Research and Map Collection 1

3 7. Add the 1911_Sanborn.jpg from the Georeferencing Tutorial Data folder. Note: you may get a window asking if you would like to build pyramids for this file, if so, click YES. Note: You will not initially see the Sanborn.jpg image in your data view even though it is listed in the Table of Contents. See illustration below. Ball State University Libraries GIS Research and Map Collection 2

4 Using the Georeferencing Toolbar to Assign a Map Coordinate System 8. Make sure Sanborn.jpg is the layer selected in the Georeferencing toolbar. Click on Georeferencing>Fit To Display to bring your Sanborn image into the extent the data view. Your map should look like now look like this: 9. Use the Scale and Shift tools, located on the Georeferencing toolbar, to line up the Sanborn.jpg raster image to the street_centerlines.shp as best as possible. Don t worry about making it perfect; just try to playing with the tools to see how they work. Ball State University Libraries GIS Research and Map Collection 3

5 10. Once you have shifted and scaled the Sanborn image you can begin creating control points. Click the Add Control Points Tool, from the Georeferencing toolbar. Starting at the left hand corner of the Sanborn.jpg image, click on the center of the intersection of Charles St. and Walnut St. on the Sanborn.jpg image and then click on the same intersection on street_centerlines.shp. The Sanborn image will automatically spatially adjust to match the points as shown in the illustration below. Note: You can zoom in and out and pan while adding control points, but the Shift, Rotate and Scale and no longer available once you add your first control point. You can press the ESC key to remove a link while in the process of creating it. 11. Continue creating control points. For the best transformation results, it is best to create a control point close to each corner of the Sanborn.jpg image, and then create a couple throughout the image, until you are satisfied. We will be conducting a Spline, or first-order transformation, so you will need to add three control points at the minimum. Ball State University Libraries GIS Research and Map Collection 4

6 Tip: For more information on types of transformations, click on Help>ArcGIS Desktop Help and Type in Georeferencing a Raster Dataset. 12. You can also match existing current building footprints (using the 2010_ aerial.tif) to building footprints on the Sanborn.jpg. To do this just change the transparency percentage to 45% in the Sanborn.jpg layer properties windows. See illustration below: 13. Open the View Link Table button in the georeferencing toolbar to view the transformation data and the residual and RMS data for each link. Notice the numbers under the Residual column. If one of these numbers is a significant amount larger than the others that means you may have make a mistake when adding control points (such as clicking on the street_centerlines.shp layer and then clicking on the Sanborn.jpg image second.) If you notice an error you can Ball State University Libraries GIS Research and Map Collection 5

7 highlight the row and click on the X to delete that control point. Click OK to close the window when you are satisfied. Tip: If you need to close ArcMap before you have finished adding control points click on Save in the Link Table window. When you open the ArcMap document again you will be able to reload the control points by clicking on Load. Saving the Transformation Information When you have created all your control points and are satisfied with the results you will either choose Update Georeferencing or Rectify from the Georeferencing Toolbar. Update Georeferencing stores the transformation information internally within the raster dataset; it does not create a new raster dataset. This tool will create an.aux.xml extension and an.xml extension. ESRI products will recognize this Ball State University Libraries GIS Research and Map Collection 6

8 extension and correctly project your raster dataset within its products, but other mapping software products will not. Rectifying an image takes place after completing the Update Georeferencing Command. When a raster image is rectified, a new raster dataset is georeferenced using the map coordinates and the spatial reference. A rectified image can be used by other mapping software projects. For this tutorial we are going to Update the Georeferencing and Rectify the Sanborn.jpg image. 14. On the Georeferencing toolbar choose Georeferencing>Update Georeferencing. This will save the transformation data to the Sanborn.jpg dataset. This creates a new file with the same name as your Sanborn image, with an aux.xml file extension. 15. Click on the Rectify tool after updating the georeferencing. Leave the Cell Size as the default size listed in the text box and the Resample Type as Nearest Neighbor and choose and appropriate Output Location and Name of your choice. Under Format choose TIFF and leave the compression type as NONE. Ball State University Libraries GIS Research and Map Collection 7

9 Tip: For more information on resampling types, click on Help>ArcGIS Desktop Help and Type in Fundamentals for Georeferencing a Raster Dataset. For more information contact: Angela Gibson, GIS Specialist BL ASGibson2@bsu.edu Please complete this tutorial by filling out the user feedback form found at: Ball State University Libraries GIS Research and Map Collection 8