Georeferencing is the process that embeds geospatial metadata into a historical map, allowing it to be integrated into modern web maps or other GIS software. Users perform this task by creating control points that link the old map with the current map.

To get started with georeferencing, the first step is to go to oldinsurancemaps.net and sign up for an account.

Project Link: Detroit, Mich. | 1929 | Vol. 11 

Step 1: After creating an account and following the link to the section of the map we are georeferencing, scroll down to the dropdown menu labelled Prepared.

Look for the next tile in the sequence (in this example we are using Page 80) and click georeference. 

Step 2: Now you should see the georeferencing interface. On the right side of your screen, the Key Map will already be generated and overlayed onto the current map. The Key Map's transparency can be adjusted with the Reference drop-down menu underneath the map.

For each historical map piece, find the corresponding number on the Key Map. For this example, that would be tile 80. 

Step 3: Once you have located the general area of where the map piece goes, you will set the Reference map to "None" and check the box labelled "Parcels." By using the historical map piece on the left, you can more specifically find the intersections that match on the present day map on the right.

Note: the Key Map should be used ONLY as a means to help find where pieces go. It is not 100% accurate so streets may be off center a bit. 

In this case we can clearly see the main streets match up with the exception of Continental St., which has been removed over time.

Step 4: Now we can set our control points for the old map on the present day map. It is best to set 3-4 points, keeping in mind that they should be spread out as much as possible to ensure everything aligns correctly.  

To set each control point you will need to click on the historical map on the left first and then place the corresponding X on the current map on the right.

The best way to keep things accurate is to use the corner of intersections with land parcels. As you can see above, we used the corner of the land parcel at the intersections of Freud St and Navahoe St.

Note: if you cannot find appropriate land parcels then consider skipping to a different map piece or asking staff for assistance. 

Above you can see how it should look once all the points have been set in the corners of the land parcels. 

Step 5: To complete georeferencing, click on the check mark in the upper right portion of the map window. The system will georeference the map and take you back to the previous landing page to do the same process over for the next piece! 

By using the Preview dropdown you can see a preview of what the map looks like over the current map to check for accuracy. Not all maps will be a direct 1:1 as neighborhoods have changed over time. But in this instance everything matches up smoothly.

If you encounter issues while georeferencing, do not hesitate to skip a map piece and move on. With big changes to certain areas over the years there are pieces that will not be possible to georeference in this context.

Some common issues that you may encounter:

• Highways or freeways obstructing part, or all, or the land parcels and intersections
• Later constructions of large factories or other buildings
• Expansion or widening of certain roads
• Road names changing
• Changes in rail lines
• The waterfront sections not matching the shoreline exactly 
• Map pieces warping in the preview (may come down to a control point on one map not matching the other)

Staff in the atrium may be able to help you with some of these. But when in doubt skip to the next one!