Week 6

Mapping on maps on maps

By Alex / October 19, 2022

I flipped through a lot of maps available on Georeferencer before finding a clearly labeled map of the Midwest with very specific labels and well-drawn roads.

Old tan map with red and black road lines and large black blobs representing major cities as well as small labels for minor towns
A segment of the map, which stretched from Memphis to Charleston.

After placing around 7 points on major city points, this is the map it created. Even though the map was well labeled, some of the roads and towns are different in 2022. This made making the map overlay difficult, even though it is clearly labeled. Therefore, everything is a bit farther north than it should be.

An old, tan map is overlayed on a new green Google Map. There is a bright orange dot where Charleston is.
An overlay of the old map over a modern Google Maps view. The orange dot represents where Charleston actually is.

Georeferencer has a cool detail where you can plot a journey using the old map, then see it on the modern map along with the number of kilometers the journey would be. I think it would be interesting to use a more accurate, georectified map to measure how long a journey would take based on the old map as compared to the journey based on the new map. One would have to determine how to measure how that length of time was calculated (are we basing it on modern vs older cars? On walking directions?) but it could be an interesting experiment. It also might be interesting to see if one could use an old map to get from one major city to another.

A dotted line stretches across a map from Cincinnati to Hamilton to Lexington, with Lexington depicted on the older map
Georeferencer’s “length” feature creates a journey.

I think an issue with georeferencing could be new borders and/or roads along with changes in terrain due to human or natural intervention. These factors could make the maps much less accurate, which might matter depending on what they’re being used for.

Overlay of the old map on the new one, showing the edge of the old map.
The very edge of the map overlay.

I think that this method wouldn’t be particularly useful if one wasn’t actually comparing maps. For example, if one was comparing terrain, this sort of map overlayed over Google Terrain wouldn’t be particularly useful.

1 thought on “Mapping on maps on maps”

  1. I agree that it can be challenging to make the map fit well with the maps that we have today. How can we know whether roads or borders have moved since the original map was made? For this reason I think its best to start by looking at more concrete features like lakes, rivers, and other natural features. Borders and roads and other landmarks can also be useful, but we can’t always be certain about their accuracy.

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