USGS Historical Maps Via Topoview

In the days before Google Earth (and similar) one of my favorite pastimes was to pour over printed maps. And my favorite maps were the large scale topographic maps produced by the the USGS, the United States Geological Survey. Back in the day we actually went to a store and bought the maps we needed and a collection of large-scale maps covering the Adirondacks was a non-trivial investment.

Going back to the mid-90s the USGS has also provided digital access to maps from its' vast library. That access has evolved considerably over the last 20 years culminating in the recently unveiled Internet application called TopoView. TopoView provides public access to (nearly) the entire library of historical topographic maps created by the agency over the past 135 years; over 170,000 map sheets from different editions (year and scale). If you want to dive right in the link goes to the TopoView home page where you'll find a short video that explains how to use the application. Or just go straight to the application and start poking around. The TopoView interface is well designed and well executed. Best of all, it's fun to use; at least I think so.

A screen capture of the TopoView interface. The box in the lower left provides details map sheets available for the selected grid cell. Clicking the map image in the box opens a high resolution image of the map. Links in the box allow maps to be downloaded in several different formats.  

TopoView is a remarkable application and, for the Adirondacks, it provides a unquie source of historical data. The Adirondack region has undergone two great transformations over the last 200 years. The first was the destruction of vast swaths of virgin forest by logging and fire starting around 1850 and lasting into the early 20th century. The second transformation has proceeded more slowly but is well underway. It is the regeneration and succession of the Adirondack forests following the  protections put in place starting in the 1890s. The maps available via TopoView provide a timeline and geographic snapshot of  that second transformation.

Let's look at some maps that illustrate what I'm talking about. The four maps that follow are:

• 1898 - USGS 1:62500-scale Quadrangle for Thirteenth Lake. The map is overlaid with two current hydrologic data sets (also available from the USGS). The red lines represent streams and rivers and the dark blue areas are represent water bodies (lake and ponds).
• 1954 - USGS 1:62500-scale Quadrangle for Thirteenth Lake, NY - with hydro overlays
• 1954 - USGS 1:62500-scale Quadrangle for Thirteenth Lake, NY - water boundary overlay is not shown to make it easier to see the representation on the topographic map
• 1997 - USGS 1:25000-scale Quadrangle for Bakers Mills, NY - a higher resolution recent map

Map 1: 1898 - USGS 1:62500-scale Quadrangle for Thirteenth Lake. The map is overlaid with current hydrological data. The red lines are streams and rivers. The dark blue areas represent water bodies (lake and ponds). The mis-alignment between this 120 year old topographic map and the modern GIS layer is clearly visible. But this map was made in the days before aerial surveys and it met the accuracy standards of the day. Quite remarkable actually, this is not easy country to move around in.

Map 2: 1954 - USGS 1:62500-scale Quadrangle for Thirteenth Lake, NY - with overlays. The modern boundary layer for the Mud Ponds aligns closely with the outlines shown on the topographic map.

Map 3: 1954 - USGS 1:62500-scale Quadrangle for Thirteenth Lake, NY - water boundary overlay not shown. Note the addition of the trail that reaches the ponds.

Map 4: 1997 - USGS 1:25000-scale Quadrangle for Bakers Mills, NY - a higher resolution recent map with water boundary and stream overlays. The current hydrological overlays align closely with the topographic map. 

I download the topographic maps using the TopoView application and loaded them into qGIS (Quantum GIS, open source GIS) so I could add the high resolution water layers that provide an up-to-date geographic context. Map one, from a USGS map printed in 1898, shows an approximation of the size, shape and location of the two ponds (Mud Ponds, in the Siamese Lakes Wilderness). But that's not to say that the map did not meet the accuracy standards of that time. Given the survey methods available then the map was very likely up to standards and accurate enough. If you wanted to visit these ponds that map could serve as your guide. While it is ultimately true for all data, geographic data is always an imperfect and approximate representation of the real world. It's easy to forget that when reading a well produced map from a trusted source. USGS topographic maps are produced to meet an accuracy standard that defines acceptable levels for accuracy and errors. You can learn more about this here.

Map two shows the same water layers overlaid on the USGS map from 1954 and, as you can see, the alignment between the USGS map and the modern water layers is significantly better. This map also shows a trail. That trail was not shown on earlier coverages of the area. Map three is the same configuration but with the display of water boundaries turned off. This makes it easier to see the ponds as they are represented on the topographic map.

Map four was made using the current base map from 1997. The newest map is higher resolution with a scale of 1:24,000. The earlier maps represented a scale of 1:62,500. The alignment of the water layers with the latest topographic map is very good. An interesting side point is that the trail visible in the 1954 map is no longer present on the map. See my post on a recent hike to these ponds to learn more about why this point was important to me.

The maps I downloaded from TopoView to create the above images were retrieved in the GeoTiff format. That format provides the highest quality option for maps retrieved from TopoView. The KML option is nearly as good and works best with Google Earth. The GeoPDF format is best if you want to print a copy of a map that you download. And the JPG option is good for viewing maps directly on your computer, especially in a web browser.

In upcoming posts I'll discuss additional opportunities and issues associated with this incredible source of historical geographic data.

Base Maps

In earlier posts I introduced the Hemlock Forest area and I talked about why I want to understand how ecological communities are changed when non-native species become fully established (look back at those previous posts for the details). I've also said that anyone with motivation can acquire and contribute valuable scientific data. What I have not talked about is what data you might get and how you might get it. The what and how will vary based on your interests but the thing I can do is to describe my project in detail. If you extrapolate from there.

As for the "what" you have to start with a question; something that interests you. I want to understand how non-native species alter existing ecological communities and species assemblages. My thinking is that in many cases these aggressive non-native species are not going away. They are here to stay. So, at what point do the invaders alter previously existing communities to an extent that a new community type is present. Most importantly, are those new assemblages of species more or less fit in terms of their capacity to provide ecological services and to resist future disruptions. It's commonly held that the general reason invasive species are so successful is that predators and pathogens that co-evolved with the invader are not present in a new locale. That is certainly part of the story but I wonder if some species are in effect "generalists" able to dominate where ever they are found. Take Japanese Knotweed for example. Once established, you can repeatedly mow a stand of Japanese Knotweed off at the ground for several years running and it will grow back with vigor as soon as you stop. And, if you are not paying attention, it will spread to surrounding un-mowed areas via rhizomes. Eventually you can kill it by depleting the energy reserves present in the roots, but Japanese Knotweed is one tough plant. Human activities have increased the speed at which plants like Japanese Knotweed are dispersed but it seems possible that this plant has evolved strategies that would allow it to spread far and wide on its own. We need to better understand how these aggressive generalist species operate because it seems likely that they will eventually be present globally where ever there is suitable habitat.

Back to the project, the first thing I want to know is which communities are present and where they are located. This is the easy part for me because my interest in this has emerged from working with geographic information systems (GIS). A GIS allows you to place your data into a geographic context. Using a GIS you can visually look for patterns in the distribution of the phenomena of interest. Going further, there are a wide variety of analysis techniques you can use to learn more about the phenomena as represented by your particular set of data. In short, I am starting the project with the creation of a GIS.

The first thing you need are base maps. As a term, "base-maps" doesn't have a distinctly defined meaning. It refers to whatever map layers are needed to put your data into a geographic context. These days we can download a wide variety of base-map layers from the Internet. Believe me, it didn't used to be that easy. And, if you are working outside of the United States, it might still be a major undertaking to get the base-map layers that you need. For my project I'm starting with a raster base-map layer created from a USGS topographic map. The USGS refers to these as digital raster graphics or DRGs. I'll be writing about where you can get map layers of various types in future posts but, for now I'll let the images tell the story.

A digital raster graphic (DRG) base layer showing the hemlock forest. The red line delineates the boundary of the land that is included in the Saratoga Spa State Park. The orange line shows the marked trails coming from the parking area on Crescent street (upper right in the image). Notice that in the lower left portion of the image the red boundary line does not follow the boundary visible in the underlying DRG. The boundary line was digitized from a map of the State Park and there is a slight discrepancy between the two sources. This could be the result of the two sources using different surveys or it could be a cartographic discrepancy coming from differences in the scale and accuracy represented by the two different sources.

I have also acquired aerial imagery of the Hemlock Forest Area; orthoimagery made available for public use by the New York State GIS Clearinghouse (see the Mystery Lines post for more information on this imagery source). The images are geo-registered and line up pretty well with the underlying topographic map layer. My data will be layered on top of the background provided by the DRG and the orthoimagery and I've started by creating a layer containing the park boundary and the state maintained trails present in the forest.

Image Two: The Hemlock Forest aerial image base layer with park boundary (red) and trails (orange) superimposed. Many details emerge from this view of the forest. For one, the old growth hemlocks that provide the area's namesake are easily seen clustered in the area circled by the upper trail loop.   

My interest is in ecological communities so I need to know what communities are present and where they are located. That information is available in a map published along with the Spa State Park Master Plan released in 2009. The ecological communities map is provided as an image in a PDF file. You can't add this PDF to the GIS directly but I was able to take the image and register it with the base maps in my GIS. I'll document the process used to do that in a future post but images three and four show the results A key feature of the GIS software is that it allows you to control the level of transparency used to display each layer.

Image Three: The ecological communities map registered in the GIS. I grabbed the image from the PDF using standard screen capture software. The screen capture was saved to a JPEG format image file. That file was added to the GIS and registered with the base-map layer. As seen here, the ecological communities layer is displayed as a non-transparent layer; you can't see through it but you can see the base layers around the edges. The boundary and trail outlines are visible because that layer is displayed on top of the eco-communities layer. Each colored area represents a different community type and the zones can be interpreted using the legend found in the original document. 

Image Four: The same map with the eco-communities layer set be partially transparency. Now we can see through the eco-communities layer to the underlying imagery. Using the GIS in this way each additional layer provides more information and seen in combination patterns that were not previously visible become apparent.

There's one more layer that I need for may base layer set. That is a layer of just the outlines of the community zones created in a way that will allow a database table row to be linked with each zone. This linkage between map objects and data is what GIS is all about and this capability will provide the basis for future analysis. I created the layer by "hand digitizing" the ecological community image; essentially I traced the outlines of the zones using tools provided in the GIS. The window seen in Image Five shows data associated with the object selected in the map (the blue area in the center). I'm just getting started, so I have only a couple of columns in the database table. But now that the linkage is in place I can add more columns as I need them.

Image Five: The complete base-map set from the GIS. The black outlines are the zonal boundaries for the various ecological communities identified in the Spa State Park master plan. Each outlined object is linked to a row in a database table. This allows the map representation of each ecological community to be associated with whatever data we want to capture.

Reference and Resources:
The Spa State Park Master Plan Eco-communities map

Mystery Lines: What are those lines seen in the satellite images?

I love to visually explore an area using Google Earth (or similar software) and then go off and match up what is actually present on the ground with what I could see on the computer. Google Earth provides easy access to high resolution images but, if you are willing to dig a little deeper, there are many other sources of spatially referenced data that can be analyzed to learn about areas we want to study.

But let's talk specifics. Looking at satellite images of the Hemlock Forest area I noticed that there are some odd looking parallel formations present in one area of the forest. You can just make them out in the image from Google Earth (Image One). What are they? What process created them?

Image One: The lines are seen in the center of the image running at a 45 degree angle from upper right to lower left. The straight line that runs from top to bottom is a stone wall. Source: Google Earth, Historic imagery from April 1997.

Viewed in Google Earth I couldn't see enough detail to come up with a plausible explanation for what the lines represent or how they were created. But, for locations in New York State, other options exist including the very high resolution orthoimagery available from the New York State GIS Clearinghouse (NYSCG). Orthoimagery is a fancy name for aerial photographs; pictures taken from airplanes using high resolution cameras and techniques that minimize distortion. When you take pictures of the earth from a satellite the distance between the satellite and the ground pretty much ensures that the camera is at a right angle to the ground. So there is little or no distortion of the image. When you take those same pictures from an airplane, if the camera is not perfectly parallel with the ground, the images are distorted.

The imagery available from the New York State GIS Clearinghouse (NYSCG) covers (nearly) all of New York State and is available to the public via the NYSGC website. The catch is that there are thousands of files and they are big files. And, once you find the right images, you need a way to view them. These images are geo-referenced meaning that using the right software you can view the images and they will line up correctly with other map-based data layers. The software you use is commonly referred to as GIS; an acronym for Geographic Information System. Loaded into a GIS these geo-referenced images can be analyzed using a variety of methods. They can also be used to provide a base layer on which you overlay other data. This is much like what you do when you view satellite imagery in Google Earth and then add points or lines or outlines (polygons) on top.

The Hemlock Forest orthoimagery (Images Two and Three) (viewed using Quantum GIS) reveals a lot more detail and those curious lines now take on a distinctly man-made look. Particularly telling is the track that comes in from the left and crosses the formation (Image Three). They look like tire tracks but when taking measurements in the GIS I found that the lines in main set are about 50 yards apart. That made me think that they might be ditches created using a tractor or bulldozer. It is also more apparent from the orthoimages that the formations are filled with water. The dark color seen in the formations is the same as the color of small ponds and streams present in nearby areas.

Image Two: The lines are in the center of the image running at roughly a 45 degree angle to the top of the image. The red lines represent the boundary of the State Park. The park boundary is a separate layer viewed on top of the images in the GIS. Source: New York State GIS Clearinghouse.

Image Three: Zooming in for a closer view the structures and the "track" coming in from the left have a distinctly man-made look. Source: New York State GIS Clearinghouse

Still, I had to wonder why someone would create ditches -about 50 yards apart- through the forest at this place. That left only one solution: field trip. From the Hemlock Trail parking area twenty minutes by trail and another half hour winding my way through the swampy forest brought me to the place pictured in Image Four. This, clearly, was one of the ditches seen in the orthoimagery and it was also immediately apparent that these are ditches that someone dug.

Image Four: The ground view of one of the water courses seen in the aerial photos. Filled with debris and leaf litter these were probably a few feet deep when created. The surrounding area is a swampy, nearly level. The entire area has very poor drainage. So it seems likely that someone dug these ditches to provide drainage for some type of agriculture.

The ditches are roughly 50 yards apart and run in straight lines through the forest for two to three hundred yards. What was not apparent from the aerial imagery is that the area where these ditches are found is very flat and very swampy. A few larger and older trees are present but most of the trees are roughly the same size (and age). Based on the size of the trees I estimated that this area was probably in use for some type of farming 50 years ago.

But something was still missing. The surrounding areas were all clearly used for agriculture in the past but this area is very wet and it is surrounded by swamps. My visit took place in late November and it had been generally dry, and even so, every depression in this area is filled with water. During wetter parts of the year this area would likely be flooded. The trees that are present are types that you find in a hardwood swamp or floodplain forest.

However, after poking around a bit more, a possible explanation appeared. One of my interests is in how invasive species compete against native species so I'm always on the lookout for invasive plants and trees. And I noticed the presence of a number of small, stunted, trees interspersed among the common species. Being late November, with the leaves down, I couldn't tell right away what those trees were. Then, one of them gave up its' secret, on a branch I spotted a small apple. The stunted trees are apples trees and now I could see that someone had tried to drain the area to create an orchard.

It appears that that plan did not work out very well. Apple trees prefer well drained soil and perhaps the farmer was unaware that this area is notable for lying over a layer of impermeable clay. Not too far away that clay, combined with the nearly flat topography, has produced a type of wetland known as a "perched" swamp. A perched swamp is a wetland where the water on the surface is not connected to the local water table but where the drainage is so poor that you get a swamp anyway. In most swamps the water level rises and falls along with the local water table but this is a place where the water doesn't drain through the soil and runoff is slow or non-existent. Creating an orchard here was never going to be easy. Which may be why we now have this wonderful little wild area to explore and enjoy.

Resources:
New York State GIS Clearinghouse Orthoimagery

A little Wild: The Hemlock Forest

Things are changing. The way people think is changing. The natural world around us is changing. Everything is changing. This has always been the case; change happens. But one thing is different now. We humans are altering the global environment at a pace and scale that from the perspective of geologic time looks a lot like the great natural cataclysms of the past. Think in terms of huge super volcanoes that shook entire continents or the asteroid that killed of the dinosaurs. We are the human asteroid. We are in effect running a giant experiment on how the earth reacts to change at scale and lots of data is coming in. Our instruments and satellites capture immense amounts of data every day. Leaving us with the questions: "what can we learn?" and "what should we do?". That's the context for this blog.

OK, setting that cheery opening aside, I'm planning to write about very specific places that I think are interesting. One of those places is a small (300 acres) forest that is part of Saratoga Spa State Park. I call it the Hemlock Forest though that name is completely made up. Before going any further, let's look at a map (Figures One and Two).

Figure One: The City of Saratoga Springs, New York and surrounding areas. The green outline represents the boundary of Saratoga Spa State Park. The Hemlock Forest is on the right wedged in between Rte. 9 and the I87 (the Northway). The park covers approximately 2800 acres and that includes a tree nursery two golf courses, a Hotel and an outdoor performing arts center that seats 20,000 people (SPAC).

Figure Two: The Hemlock Forest is outlined in red. This section of Saratoga Spa State Park covers about 300 acres. The forest is separated from the main body of the Park by Rte. 9 (on the left). The northern edge of the forest runs into the rapidly developing urban/'suburban fringe of the City of Saratoga Springs. The southern margin is mostly undeveloped with a connection to the Kaydeross Creek other nearby natural areas.  

There are several interesting things going on in this little bit of forest. One is the presence of wetlands of several different types including an uncommon "perched" swamp (perched referring to how the swamp interacts with the local water table). This particular wet area, though small, hosts an uncommon ecological community anchored by the presence of old growth Swamp White Oak trees. The forest also includes an old growth hemlock forest and good stands of American Beech trees that so far have held up against the Beech Bark Disease that has devastated Beech trees elsewhere. The State Park maintains a two mile long trail that loops through a 150 year old forest that includes hemlocks, White and Red Pines, and Oaks. The existing trails provides direct access to less than half of the total area though the un-trailed southern portion of the forest is hardly an untrammeled wilderness. The entire area is crisscrossed by stone walls, old farm and field tracks, and unofficial trails. Still, parts of the forest have a distinctly wild feel and the range of habitats present make this an important natural preserve.

I enjoy walking the area and capturing data that represents the "current state" of the ecological communities that are present there and that will be one of things I'll write about in this blog. This "Field guide to the Hemlock Forest" will also include information on technologies and methods that I use, and that anyone can use, to gather real data about places like this. I'm sure that some posts will start with something like "saw a  Barred Owl today", but my emphasis will be on acquiring and managing data that represents the ecological and environmental state for this area. My hope is that this data will be useful in the future. In particular, I'm interested in how invasive species interact with native communities and I'm hoping to capture a data set that can be used to learn more about how those interactions change over time.

When I was a kid I loved to read about the explorers and naturalists who traveled the world finding species not known to western science. Unless you are willing to spend a lot of time looking through a microscope it's unlikely that any new species will turn up in northeastern New York, but spotting the arrival of a species that has not been present in the past is a very real possibility. We have tools at our disposal that were unimaginable even 20 years ago. A smartphone with GPS, environmental sensors, and on-line identification guides doesn't match a tricorder quite yet, but that's where we are headed.

If you are reading this it might be because you live nearby and can visit these places. Or maybe you are interested in nature generally and my writing is not so bad as to ruin it for you. Or, maybe, and this is my hope, you want to do something like this where you live. I'll be writing about citizen science and how we can contribute data towards a better understanding of our world.

That's all well and good but you may get an inkling that the for me this is fun. The Forest is less than a mile from my house and I like to walk in the woods. I used to play golf but, to paraphrase Mark Twiain's famous quip, "that's a sure way to ruin a nice walk." There is a parking area with trail access on the northern edge of the forest (access is from Crescent Avenue). The trails are lightly used and I'm yet to see another person while wandering off trail. Much of the area is swampy so if you do go off trail you can expect wet feet. And I'm not worried that publicizing the area will bring in swarms of hikers. For much of the year the hemlock forest is well defended by armies of mosquitoes and ticks (beware: Lyme Disease, seriously I have captured many many Deer Ticks while walking in this area). For now the Hemlock forest is well protected.

Resources:
Saratoga Spa State Park Master Plan (pdf)
Saratoga Spa State Park Master Plan Map