How to Georeference a Sanborn Map (Estimated time to georeference and correct after team suggestions: 2 hours per map)

Opening a blank map template 1. Begin by opening ArcMap. (The Icon will be similar, but will vary slightly depending on

operating system and version of the operating system on your computer).

2. On the opening page, select New Maps from the left hand menu, then “Blank Template”

from the My Templates main area.

3. Save the file with an appropriate name.

4. Click on ArcCatalog to open it if it is not already open.

5. Navigate to the location in ArcCatalog containing the DOQQ.jpg file. Drag the file and drop it into the empty map space.

6. This should result in a screen similar to the below screen capture. (If a box pops up asking

if you would like to build pyramids, click yes and wait for the process to complete. This will

allow rendering to take place faster)

7. Zoom in on the area of the aerial photo where the Sanborn map will occupy. Importing the

DRG and finding the streets that are on the Sanborn map will help find the right area on the aerial photo as well. It may also be helpful to have a map open (like Google Earth) to have street names labeled while georeferencing. You can use the coordinates on the bottom right corner of the ArcMap page to get close to your desired location in Google Earth then identify

the streets around the location.

8. Navigate back to ArcCatalog within ArcMap and drag the Sanborn map you will be georeferencing into the map frame.

9. A notification will pop up to ask if you would like to build pyramids. Click “Yes.” (As was above, This will allow rendering to take place faster.)

10. A second notification will pop up to alert you that the layer is missing spatial reference

information. This is okay and the reason we are georeferencing so Click “OK” and move on to step 11.

11. Select the Sanborn map on the georeferencing display (the map will begin with 1920_).

12. Next, on the georeferencing toolbar, click Fit to Display.

13. Select properties of the Sanborn map (1920_03b map) from the table of contents.

14. Click on the display tab.

15. Change the transparency to 50% then click okay.

16. Use the rotate, shift and scale tools on the far right of the georeferencing toolbar to further

align the Sanborn map.

17. In the Georeferencing Toolbar select the “Add Control Points” Button

18. Click on the View Link Table

19. Verify there are no links in the table, the Auto Adjust block is checked, and the

Transformation drop down contains 1st Order Polynomial (Affine).

You can close the table or work with it open depending on your personal preference.

20. In the Georeferencing Toolbar select the “Add Control Points” Button

21. Open the magnifier tool and set to approximately 200%.

22. Move the magnifier tool over the first suggested control point location and place the first

from control point on the Sanborn map.

23. Uncheck the Sanborn map layer and place the “to” control point on the same location on the

orthoimage.

24. Turn the Sanborn Map layer back on and repeat with at least two more Control Points. Note: While the Affine transformation will work with three points, it would be beneficial to do at least four points, placing the points as close to the edge and as far away from each other as possible.

25. Once the Sanborn and aerial photo visually line up, click on the georeferencing pull down menu, select update georeferencing. The Sanborn map in now georeferenced.

26. Open the “View Link Table” to check your control points.

27. You can look at the RMS error. If the RMS error is extremely high, go back and recheck the

georeferencing. Also if you accidentally add an incorrect point, you can delete it from this

table.

Ways to Prevent Digitizing Errors:

Feature Classes

1. Enable “end snapping” and “edge snapping” in the snapping toolbar so that you do not undershoot or overshoot when connecting polylines or polygons. For our purposes, set the snapping tolerance to be set at the default 10 pixels.

2. Use Auto Complete Polygon when creating a polygon that shares a border with an existing polygon to avoid gaps and overlap

3. Under the editing toolbar, set the “Sticky move tolerance” to 10 pixels. This will help prevent inadvertently moving a feature when simply trying to select it.

4. Before starting to digitize each feature, we want to make sure the layer we are editing is added as the feature template in the Create Features window.

5. Zoom in at a smaller scale (but not too close) when digitizing. 6. Make sure to snap all the roads to the boundary layer. 7. Split each road into blocks to allow for geocoding with the left and right start and end

address numbers for each block. 8. Add the road width for each road/block, however it will still be a line feature (not a

polygon feature class). 9. When creating polylines or line segment use the Editing Toolbar tools such as Straight

Segment or the tool that allows you to trace the outline of another shape 10. Make sure polygons do not have loops

Attribute

1. Columns should contain single info on a single subject 2. Keep a primary key so you can use it to join tables and identify unique variables 3. Keep the attribute table tidy and delete any unneeded columns or mistake columns 4. Do not have columns in the attribute table that have info that relies on another column in

the same table

5. Keep redundant columns to a minimum 6. When finished digitizing a feature, enter the attributes by clicking the “Attributes” tool in

the editing toolbar. 7. Make sure any null values have a value entered in. In the cases with height and not a

number of stories (or vice versa), leave blank and calculate the field later. (Or manually calculate it immediately, but it may save time several fields are empty to make the calculation later using field calculator.)