Overview
Data Structure
Digitizing
Data Entry Errors
Level of Effort
Error Analysis
Metadata Report
Future Mapping

Digitizing Procedures

I. Sanborn Maps Image Files:

1920_02A.jpg—Randy Estrada
1920_02B.jpg—Patricia Laird
1920_03A.jpg—Henry Roberts
1920_03B.jpg—Brenton White

II. Georeferencing Steps

1. Prepare the orthophoto projecting its coordinate system in ArcCatalog. Right-click on the filename and go to: Properties/Spatial Reference/Edit. Select UTM-NAD 83 UTM Zone 17. It is critical to add the orthophoto FIRST, in order for it’s coordinate system to set the coordinate system of the data frame. Alternatively you could explicitly set the data frame coordinate system via the Properties dialog, but this is not recommended.

2. Start a new blank ArcMap document adding from ArcCatalog these files:

1. 038078a48.sid—Charlottesville’s photo image

2. 038078a4.tif—DRG Image

3. 1920_02A, 02B, etc.—The Sanborn map.

3. In the Georeferencing Toolbar, make sure the Layer is the Sanborn map image.

4.With both, the DRG as features’ reference and the orthophoto together, zoom in at the scale 1:2,000 to the orthophoto’s assigned area.

1. Turn off the DRG image to see the orthophoto assigned area, having used the DRG as reference.

5.Click off Auto Adjust in the Georeferencing menu so as to avoid jumping the photo and the image.

6.With the Sanborn map layer active (1920_2A, 2B, etc.) at the top of the ArcMap program, zoomed in at 1:2,000, then, go to Fit-to-Display in the Georeferencing pull down menu.

7. On the Georeferencing Toolbar, select the rotate icon and rotate the Sanborn map 15 degrees and move that same map to the assigned area with the Shift button.

1. a. Right-click in the Sanborn Map in Properties/Display/Transparent, set the percent to 40%. Then, click OK.

8.Open the Magnifier Window at the top of the program. Right-click on the Magnifier title bar and set magnification to 200%.

9. Establish Control Points with the Add Control Points icon in the photo. Open the Link Table to see the added control points.  You must click on the Sanborn map image location FIRST, then on the corresponding location on the photo.

1. Affine Transformation (First order transformation) or Warping Transformation (second transformation method)

2. Ignore RMS value as it has no diagnostic value in this case

10. Activate Auto Adjust in the Georeferencing toolbar to see the effect of adding the control points.

11. Finish the Control Points with Update Georeference (in the Georeferencing pull-down menu).

12. In the Georeferencing pull-down menu, click Rectify, then Save the image as TIFF (.tif) file.  In this case, if you provide a smaller cell size you will cause the type that is on the map to be more legible in the Rectified version.

III. Several of the buildings on the Sanborn maps share walls (multiple uses in a single building) and the street centerline layer is intended for use with a geocoding service. In each case, what special digitizing settings/considerations must be used/taken into account?

Buildings: With the buildings sharing the same walls, we would want to use the auto complete polygon task. We want to use this when a polygon shares a common boundary.

Note: Another technique to consider is to use the Cut Polygon Features task. You would be able to first digitize the outer walls of a structure, insuring that they would be continuous and straight. Then you could “cut in” the internal partitions.

Use “AutoComplete” to avoid overlapping geometry for buildings that share a common wall. Once we combine the database and maps into one unified whole, we need to have the streets centerlines work as a unified structure, we need to edge match using an endpoint select and then merge.

Geocoding services: The Sandborn map and .tif reference map contain information on the following address fields:

• street number

• street name

• street direction (e.g., NE)

• street type (e.g., St)

Since zip codes are not available, we need a geocoding service that is based on these four fields but does not require zip codes. We could use one of the following three geocoding services (in the choices available in ArcCatalog, we want to use the geodatabase format instead of the file format):

• US Streets geocoding service style

• US One Address geocoding service style

• US One Range geocoding service style

When it comes to the street centerline layer, the directions in which the lines, representing the streets, are digitized matters when it comes to the functioning of a geocoding service. In other words, the lines need to be created such that the FROM end of the line corresponds to the low end of the address number range, and the TO end of the line corresponds to the high end of the address number range. If this is not the case, the interpolation performed by the geocoding service will be in error.

GEOG 5223: Elements of GIS: Part 2 (ESRI Track) CD. Accessed September 2004.

How to Read Sanborn Fire Insurance Maps, University of Virginia Library website. http://fisher.lib.virginia.edu/collections/maps/sanborn/web/details.html.  Accessed September 2004.

GEOG 5223: Project 7, 8, 9 & 10: Final Project, Accessed September 2004.