We love to pour over old Sanborn Fire Insurance Maps and it turns out that there are several publicly available sets of maps for Louisville in 1892, 1905, and possibly some other years. Patrick Piuma has been painstakingly stitching sheets together to build larger area maps for research and nerding out.
1. Stitch together map sheets to cover the area of interest.
The process starts with collecting the necessary Sanborn map sheets for a particular part of town. Typically the map sheets covers a couple blocks. The hand drawn maps are surprisingly accurate once overlaid on digital aerial maps. The high resolution map sheets have large file sizes, which is good because the tiny written notes wouldn't be legible at lower resolutions, but this presents a problem when pulling together twenty or more sheets in a single Photoshop document. We've found that reducing the full resolution sheets by 50% when making large area maps is doable and still retains print quality resolution for legible notes etc, though the photoshop documents are typically hovering around 1GB while working on them. Also gets really tricky when you are lining up the sheets. Depending on what your final use of the document is will determine how much time you want to spend cleaning up the map overlaps. Though the buildings usually line up pretty well, the dashed water pipe lines in the middle of the streets almost never do.
At this point you have a great map to review and can stop here. If you are a gluten for punishment you can continue to the next steps.
2. Trace the building footprints in Illustrator.
This part requires diligence and a little carpal tunnel syndrome. If anyone knows an easier or more accurate way to do this we would love to know. Basically you want to make sure your stitched maps are as squared up as possible using guide lines etc in the Photoshop phase. It is important that everything is squared up because you need to be able to trace the building footprints with right angles whenever possible and make sure that you close your paths to form the individual buildings as well any details such as where there is a camelback roof on a shotgun that is taller than the rest of the building.
At this point you have a pretty interesting graphic representation of the plan view of the city blocks and could stop here if you like figure-ground images (we do).
3. Massing models in setup.
Here is where having some familiarity with the software will be important to make sure that even these simple massing models are well built by starting with .dwg files exported from Illustrator of the building footprints. Starting with a solid base map of streets and blocks is critical so you can line up your building footprint layer and get that squared up from the beginning.
4. Extruding the footprints.
Once all of the footprints are in Sketchup and they each form individual closed polygons you then have to go through the process of looking at the original Sanborn map an use the detailed building height information to extrude the buildings. Sometimes the map only indicates the number of stories the building is, such as 1 or 4 etc. Many times there is actually a second number such as building is 4 stories and 50' tall. When there isn't a building height indicated we standardized buildings to be 12' for each story. This may be a bit generous, but we noticed on average when both numbers are given that it is fairly representative, plus the final model is a massing model and at some point you just have to make a call.
We aren't sure when we will get back to the 1905 Downtown Louisville model we started, but instead of leaving it on a hard drive gathering dust, here is the model you can download and play around with as you like.