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Mapping the World and Its Data

A free useful tool such as Google Earth can help with your research by allowing you to compare places over time at the same scale.


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Okay, okay, we are not going to map everything in the world and what is on every square inch. But newer technology has made it easier and cheaper to do rubber-sheeting of maps onto one another for research purposes.

And what is rubber sheeting? Besides sounding like a rather strange term, it refers to the process by which a layer is distorted to allow it to be seamlessly joined to an adjacent geographic layer of matching imagery. What does that mean in English? It means that two maps of the same place can be compared over time and at pretty near the same scale, even though they may not have been drawn that way.

An example will show how useful this can be At a recent conference, an instructor showed the class how to do this on the cheap. There is software that can do this (one is ArcGIS, which seems to be priced at $1,500 dollars), but someone can do it themselves for free using only a browser and Google Earth, also a free program.

The way is works follows. In this example the instructor found a picture in an old atlas of Saratoga County, NY of an area called Bloodville. No, not because it was the site of a massacre. but because an Isaac Blood had an axe factory there. Just imagine it - Blood Axes, but that's another story.

What was done was to find an older map of an area, in this case a Saratoga County, NY map from the 1870s, which had an inset and large scale map of Bloodville. (It is now a suburban area of Ballston Spa, NY). That map of Bloodville was saved to the computer desktop. Next, Google Earth was started up. That is a free download from Google, and it runs on both Mac and Windows machines. (We didn't try this using Google Maps, which can also be useful for research). At that point Google Earth was moved in and out until the area of Bloodville was as close as one could naked-eye to the same scale as the old map. While this seems to be a bit haphazard, remember that it is free, and not over a thousand dollars.

There was a distinctive curve in the road and the river, and the eye-balling of the common points of reference were done. The next step was to choose the "add image overlay" tool on Google Earth and select the older image from the 1875 map. It was dragged to the place where it fit the best on the modern Google Earth map, and the Google Earth map was adjusted in and out so that the fit was as good as one could get it by eye-balling.

At this point the image was fixed onto the Google Earth underlying map by clicking it. A useful tool then comes into play, which allows the user to adjust opacity of the overlaid image. This means going from completely transparent to completely opaque. By sliding the tools back and forth, one can see where the houses, barns, cemeteries, churches, roads and other geographic items were located back in the 1870s, and what's on that land now. While this was done for the axe factory, it could also be used to overlay a cabin, a cemetery, and school or any other items which appear visibly on a map, and can then be plotted onto a modern map. Even where roads and paths were could give a location of genealogical import. Obviously, this would work better in a less developed area then the downtown of a city, if only because you cannot walk through an office building and ask to dig into the wall to find the older underlying item (although this could give a clue as to where things might have been).

And if Google has done a drive by of the area in which you are interested, you can see what the houses and area looks like now. By "now" I mean within the last couple of years. Rochester, NY had a fast ferry to Toronto, Canada which stopped back in 2005, and the boat still shows up on Google Maps. So one has to be careful of recent changes. In the case of Bloodville, the area has been filmed by Google Street View, and one can invoke that on Google Earth and see what the road the river is there now, including what might have been Isaac Blood's house nearby and so on. That's a very neat tool to use, and as we have discussed, it's free.

Source Information: GenWeekly, New Providence, NJ, USA: Genealogy Today LLC, 2008.

The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of Genealogy Today LLC.

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