Web-mapping tools are great! They have revolutionized the world of maps. From Google and Apple maps to ArcGIS Online to countless other government agency, institutional, and homegrown web-mapping applications that put a startling amount of data and information at your fingertips, web-mapping has changed the world.

If you live in the U.S. (and many other places), you can now easily zoom in to your house and see whether your car, (or your neighbor’s car), was in the driveway when the plane or satellite flew stealthily overhead and took the picture that you (and everyone else), can now see on your computer screen. You can probably also see what date and day of the week the image was captured and possibly even the time?! But most people don’t pay attention to this “metadata” so we mostly avoid any conflicts that this kind of information could create.

You can transport yourself halfway around the world and get as good a “feel” for a place (short of employing virtual-reality), with maps, images and street- and birdseye-views as you could ever expect to without actually visiting the place in person. You can even peruse cartographic depictions of the world as it once was through large repositories of digitized historic maps like the David Rumsey collection that have been posted online and georeferenced (i.e. put in web-map space), by you “the crowd”. With a web-mapping tool at your disposal, connected to a large database of geospatial data the possibilities can seem boundless. Or are they?

I can distinctly remember when GoogleEarth (figure 1) launched the historical imagery time-slider in 2009. They used Las Vegas, NV (or at least my first exposure to it was inspecting the Las Vegas, NV area), highlighting the new functionality of their tool with aerial photography dating back to 1950. It was so revealing to be able to slide the bar back and forth and examine the amazing urban growth that has taken place over that time-period in this area — it was like being able to instantly go back in time 60 years with the detail of very tactile things like individual homes and streets that are often blurred over in most satellite imagery captured prior to about 2000.

I thought this kind of functionality would take off, but it hasn’t?

Here is a screenshot from GoogleEarth Pro (taken March 22, 2018), for my hometown of State College, PA with the time-slider enabled that shows for what time-periods there is imagery available from within this web-mapping tool. In case it’s hard to see in the figure below, it shows 7 imagery dates available going back to 1994, and then nothing…crickets.

 

Figure 1. A screen capture of Google Earth Pro with time-slider enabled

 

Maybe I am showing my age, but 1994 doesn’t seem like ancient history? The GoogleEarth Engine Timelapse tool pushes the time-period of imagery at the touch of a button back to the mid-1980s and impressively does so globally, but at a moderate spatial resolution from satellite imagery so that zooming in on things with a personal touch like individual homes is out of reach.

How is it that I can overlay contemporary geospatial data on top of a geo-enabled map of the world from 1812 using the ArcGIS Online Living Atlas collection for example, but I can’t look at imagery of my hometown from the 1960s? What if you study spatial patterns of post-WWII suburban development in the U.S., or merely want to see how big a garden the prior owners of your home maintained in their backyard before your family bought the place in the 1980s? Have you ever noticed how web-mapping tools for most places go silent for time-periods prior to the mid-1990s?

The answer lies mostly in a formatting problem. Like most modern geo-technology applications web-mapping tools are data hungry and they want the data in a specific format and structure. In the U.S., we have a pretty lengthy history dating back to at least the 1930s of well-organized and comprehensive aerial photography missions with multiple revisits for most places. The goal of these missions was to capture high-quality and accurate geospatial data and information (it is often called “vertical photography”), so the photogrammetrists in charge did very sciency things like carefully calibrated their cameras in the lab before going out in planes, did their best to fly at consistent altitudes, and captured multiple overlapping images of the same place so that they could produce images (i.e. maps), of places with as little geographic distortion as was possible. The “data” was captured on film and recently more and more of this film is being digitized and made publically available online. So why aren’t they viewable in web-mapping applications?

The formatting problem isn’t one of analog versus digital, but rather is one that requires 2 steps to correct: 1) Remove the geographic distortions inherent in the native film that arise when you take take a camera up into a cold plane and take pictures of bumpy objects from different angles that are not directly overhead; and 2) Tie those images very accurately to a geographic frame of reference that can talk to web-mapping applications so that things line up the way they should. The methods for resolving both of these issues are well-known, but are labor intensive and you really need to do both steps in order to get very good results. There is also the issue that aerial photographs individually cover small areas on the ground and when digitized to a high-quality (i.e. an image with lots of pixels to show detail), produce very large file sizes — but then again it is 2018 and computers are fast and storage cheap so I really don’t consider these to be insurmountable hurdles.

Consider the following great example (from this source, by Patrick Cines), of a change over time gif animation of Penn State’s campus that manually and accurately overlaid each historic image on top of the modern distortion corrected images. Watch the animation a few times carefully — can you see when the images transition from being kind of jumpy to being much more consistent? By jumpy I mean that distances and directions from one landmark to the next don’t seem quite consistent. It’s a little hard to separate the differences caused by actual landscape change versus imperfections in the imagery, but I hope you see what I do, which is that the distortions in the first 3 images are a major distraction from trying to qualitatively assess actual landscape change over this time-period. In spite of these imperfections, there was a lot of public interest in this article evidenced by it being “liked” on FaceBook over 100,000 times in the first 12 hours after it was posted. I’m not very savvy with FaceBook, but that seems like a lot of interest compared to very humble public interest in most of what I do day-to-day?

 

 

Like other examples discussed in this post, the imagery transitions from being in the format of “dumb” digital pictures to being “smart” geospatial data in the image labeled 1992, (even though I think this is mislabeled and should be 1994).

The “data” (i.e. high-quality vertical photography that has largely been digitized), is available for much of the U.S. (and a lot of the world I think?), and for many time-periods prior to the mid-1990s it’s just that the work hasn’t been done to reformat it for the greater good and unfortunately, the people that do know how to do this don’t seem that interested? My first opportunity to learn this lesson happened when I was working as a Postdoctoral Research Associate at Montana State University studying the ecological impacts of climate change (past, present, and likely future), in the Northern Rockies and Greater Yellowstone Ecosystem. One of the ways that climate change was thought to have already impacted the Yellowstone area over the last 50-80 years was by drying of subalpine meadows, which allowed conifer trees to encroach on the meadow grasses and forbs and generally shrink meadow area. This was a perfect project for geographic information systems (GIS) (of which web-mapping tools are a subset), all we had to do was find some old aerial photographs on which we could “see” the subalpine meadows and measure their areas through time. To my surprise at the time, I found a wealth of really fantastic old aerial photographs that had been captured by all kinds of different agencies for all kinds of reasons and we were off and running. With the photos in hand we then had to undertake the 2-steps described above to incorporate them into our GIS for analysis and I already knew how to do the first part so things were still looking promising. The problem was that when I asked people who knew how to do the second part they either told me that it couldn’t be done or was a waste of time. Without the ability to accurately measure things like subalpine meadow area we were a bit stuck. Combine this with the experience of a friend and colleague at the time who had just had a manuscript rejected by the journal Ecological Applications for not having addressed the 2nd step in a similar study and we were unsure how to proceed? Research funding cycles are short and we were forced to move on, not having anticipated this methodological hurdle and lacking the resources to address it. In retrospect this was a missed opportunity, but it did pique my interest in these old aerial photographs and I love it when people tell that something can’t be done — to me that rings bells as an opportunity.

So, with the interests of researchers and the interested public in mind, we are taking up the challenge of turning historic aerial photographs into geospatial data for use in web-mapping tools and GIS. We’re doing this for the state of Pennsylvania by doing 2 things 1) Acquiring high-quality scans of historic aerial photography as they become available from the agencies that curate them, and; 2) We’re developing methods to efficiently georeferenced and remove the distortions from the photographs, capitalizing on every new computer shortcut and automation trick available.

I have two primary hopes for this work. First, I hope that others also take up the challenge for surrounding states and elsewhere. Imagine if someone did the same for New York, and someone else for New Jersey, and another for Maryland? Do you want to know how land use has changed in the Chesapeake Bay Watershed over the last ~70 years? Maybe it won’t be “done” after this kind of effort, but we will be a whole lot closer to being a research question that can be answered within a single funding cycle. The State of Delaware’s Environmental Monitoring and Analysis Center has done some interesting work here. Second, I hope that the availability of these data stimulate and inspire new research questions and new students of geography and geographic data. I don’t pretend to understand all the different ways that these data could be used, but I do hope that people who are smarter and more creative than I am will come up with some great ideas.

Up next are a series of posts about some of the imagery that we are acquiring, what we plan to do with it, and early results of our efforts…