ArticleA behind the scenes look at the process of georeferencing
Many people use our collections to look at old maps and atlases of familiar places. They want to see what the place looked like in the past, and the reverse is the same, people who look through old maps wonder what those places look like today. Here at the Leventhal Center, we’ve created tools like Atlascope to answer these questions, using georeferencing to line up the historic maps with modern ones. As older maps are typically inaccurate in their proportions, the maps must often be warped to match the modern landscape. To do this, points of alignment are chosen to correspond with each other on both maps, stretching or compressing the map so each historic street aligns with its modern counterpart.
This past month, I was able to georeference this Atlas of the towns of Topsfield, Ipswich, Essex, Hamilton and Wenham from 1910. The atlas contains 35 maps of the five towns and depicts the property lines, ownership, and materials of the buildings, among other details. It was quite an exciting project to spend some time with because I’m very familiar with the areas that they depict. I grew up in Ipswich and spent a fair amount of time in the surrounding towns. Previously, I had used Allmaps, a web tool specifically designed for georeferencing maps in digital collections, to georeference maps of East Boston but nothing I was as familiar with as my own hometown.
Read more about Allmaps in this interview with developer Bert Spaan
Spending many hours poring over maps of such a well known place was really exciting. My knowledge of the town coupled with its resistance to change meant that the historic maps of Ipswich weren’t all that difficult to line up with the modern map. However, I did learn four important lessons while georeferencing my hometown.
Upon first glance at the downtown area and its tangle of streets, I knew that Ipswich hadn’t changed all that much since 1910. All the streets are paved now, but by the time the atlas was made, many of them had changed into their final configurations and erected the buildings that still stand today. Ipswich is littered with houses built in the 18th and 19th century that are well documented by the local historical society. These historic buildings create plenty of places to lay down points to “stretch out” the map. These familiar places gave me a clearer starting point for the more densely organized parts of town. If you’re georeferencing a new town, researching historic landmarks or historic districts might be a good place to start—Ipswich has several Architectural Preservation Districts in the downtown that correspond to high numbers of still-standing historical buildings, such as the Ipswich Hosiery Mills, half of which still stands in use as an office building.
In addition to providing detailed depictions of the houses in Ipswich, the Atlas also denotes building material, details like ponds, rivers, town boundaries and property lines. Many of these aren’t that helpful for placing the maps on the modern landscape, but once in a while, things line up. For example, Mr. Palmer’s property lines in 1910 line up exactly with the park boundaries on the modern Open Street map because he bequeathed his property to create Bradley Palmer State Park. But with other features on the map, it can be a good idea to double check before trusting them.
Using the familiar historic houses of Ipswich was very helpful for georeferencing—but there’s also a caveat that prevented me from relying on it too much. In Ipswich, sometimes houses moved. The most famous example would be the 17th century Whipple House, which is conspicuously absent from the South Main Green on the 1910 map . The house was actually moved to its current location from across the river in 1927 in order to preserve it.
Occasionally I would look for houses that I knew were built before 1910 only to discover that they weren’t in the same location on the Atlas. There are a couple of historic houses along this stretch of East Street now called Jeffrey’s Neck Road that I was familiar with, but upon consulting my local historical societies website, I learned that they were actually moved to their current locations in the 1940s. Talk about complicated!
Of course, while some things that are there today aren’t represented in the past, even more things that existed in the past have been removed, torn down or destroyed. Ipswich, Essex, and Hamilton all had streetcar lines that provided means for people to get around town, an interesting piece of history to see from a place where public transportation barely exists today. Some of these pieces of former infrastructure that are long gone from the modern street map have left their mark in the landscape like little ghosts.
While long gone from Open Street maps, the Topsfield branch of the Boston and Maine RR which was converted into a bike trail is still visible on satellite maps. And while the Essex branch of the Boston and Maine did not get the same rails-to-trails treatment, you can see see the ghost of the railroad tracks cutting a trail across the marsh.
One of the benefits of knowing the landscape you’re georefrencing is that sometimes there are “ghosts” that you wouldn’t think to look for unless you were familiar with it already. This was how I georeferenced Pineswamp road , which once looped all the way around to Linebrook road but now stops in the middle of the forest. Unlike the Topsfield rail trail, there’s no easy way to see the remnants of the road from zoomed out above the trees—but my familiarity with the landscape allowed me to identify the small gap in the trees that marks the entrance to the road. A detail many wouldn’t have been able to identify unless they’d walked the wide unpaved trail themselves.
One of the most surprising remnants I used to georeference this atlas was a little circular driveway located in front of a building once owned by a Professor Swain . In one hundred years, the people who’ve lived there have changed time and time again, but the driveway still curves the same little rotary into the landscape.
While georeferencing some of the more remote corners of the map, where streets were sparse and still-standing houses even sparser, I was tempted to use the winding path of a river to match points up. But remembering one of my favorite maps—a series of the Mississippi River’s meandering path over time—made me wary of such a thing. Rivers like to shift their courses over time unless constrained by human influence. Another example is this map of the Rio Grande’s course over just 50 years.
In fact, water is one of the most notorious pieces of the map that you want to avoid using. For instance, the path of the river on this Atlas Plate doesn’t look quite the same in the modern day.
Rivers have a tendency to meander over time—to change their shape and the landscape around them—when humans haven’t intervened. Old bridges were rather useful for pinpointing places along the river’s path that have remained the same, just make sure it’s the same bridge and it wasn’t replaced or washed away by a flood (like the bridge in front of the Ipswich Mills) On the other hand, this old bridge over the marshy Essex River on Essex Road (now Old Essex Road) was a helpful point in a very empty landscape.
While poring over this atlas, I got the chance to notice all sorts of unique details about the history of my town—like 16 Elm Street, which was moved to the Smithsonian in Washington D.C. or the location of gas works where a parking lot now is. I even encountered markings that I had never seen on a map before at the Myopia Hunt Club which turned out to be the grounds of the golf course. You never know what you might find while georeferencing!
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