Creating a Web Map Mashup

The strength of GIS is its ability to organize, overlay, and display multiple maps and large databases in a dynamic information system. Once environmental historians have assembled a GIS project, they can use it to find a location, identify current place names and land use in that location, query historical population data in a census table, quickly identify all locations with similar attributes, measure distances and areas, observe changes in the natural and built environment, and so on. Overlaying historical maps in the form of rasters enables quick comparisons between multiple time periods, or multiple perspectives of the landscape in a single time period. A web map allows the same sort of interaction with the primary documents to take place in a classroom setting or as an embedded map in a course website. We created two types of web maps for GeoWatch events in 2011. The first was an elaborate overlay of multiple historical maps using proprietary software and the assistance of Service New Brunswick’s mapping teams, and the second was a lightweight web map that used open source tools to overlay historical maps onto Google’s modern map.

In order to make a historical map mashup you will need the documents themselves and mapping software. Once the maps have been digitized, imported as rasters, and made “GIS-ready,” you will also need a program to “tile” the rasters for display online. This allows large map images to open quickly at multiple scales. Depending on the zoom level, it is not necessary for a browser or mobile device to download the entire map, and tiling frees up processor power by only calling up the sections of the map which actually appear in the browser window. Finally, you will need some way to serve up the maps with onto pre-existing web maps such as ArcGIS.com or Google Maps. In the first example, I will show how historical maps of St. Andrews, NB, were uploaded to GeoNB’s web server, and in the second example I show how to host files on a personal website so that they appear as overlays on a Google mashup.

In the first GeoWATCH event we had a number of digitized maps of the town of St. Andrews and we wanted to let the participants of the Canadian History and Environment Summer School explore the maps as overlays before setting out on foot to “groundtruth” our observations from the workshop. The problem was we did not have access to a computer lab, GIS software, or even internet until about 30 seconds before the workshop began. These barriers made it impossible to load historical maps and GIS files onto computers with the standardized equipment and technical support that come with teaching in a university lab environment. We needed a web-based solution. Even on-campus history classes which are usually too large to fit into a computer lab could benefit from this kind of solution. With an internet connection established and a good number of workshop participants with personal laptops most people were able to navigate to the GeoNB web map and explore the historical documents online.

The following map of St. Andrews, part of the 1878 Atlas of the Maritime Provinces of the Dominion of Canada, was full of clues to the town’s environmental history, and became the centrepiece of the groundtruthing component. We layered this map, and a selection of 1949 Fire Insurance Plans, with the current outline of the province’s coastline and salt marshes, in order to compare changes in the waterfront and urban landscape. Then volunteers led walking tours to different parts of the town, from the Eastern Commons to the hotel golf course, from the salt marshes to the commercial waterfront. For example, the group that explored the eastern commons area compared the historical outline of the rail yards, on the left half of the image, with the modern orthoimagery, roads, and land use layers for that part of the town on the right.

Eastern Commons, St. Andrews, NB showing historical overlays on left and GeoNB data on right

Eastern Commons, St. Andrews, NB showing historical overlays on left and GeoNB data on right

After the digitized historical maps had been given coordinates in a GIS, the georeferenced rasters were sent to Service NB and the UNB Geomatics Department who posted them directly to their copy of ESRI ArcServer. Then Service NB sent us a URL for the workshop participants, and we were able to focus the workshop on observing the differences between late nineteenth century features (Roe Brothers), mid twentieth century streetscapes (Fire Insurance Plans), and the current topography visible in GeoNB’s features and aerial photos.

Once the rasters were hosted on ArcServer, Service NB was able to tile the maps and post each one as a new public layer on ArcGIS.com. Then, anyone who knew the name of the layer could find it and add it to any combination of layers in the St. Andrews area. This allowed for flexible, custom web mapping. We added Service NB’s layers for parcel boundaries and civic addresses, and we were able to identify specific properties in the landscape and trace how they had been merged and subdivided over the last 133 years. Uploading the tiled maps from ArcScene to ArcGIS.com also meant that participants with smartphones supporting the “ESRI ArcGIS” app could bring the historical map along with them, zooming in and out, exploring the nearby features, and, maybe most important, “locating” themselves on the historical map using GPS (Global Positioning System). This was our first taste of mobile mapping, and I will explain more about the next stages in the third post in this series.

1878 historical map overlay and GeoNB data for St. Andrews NB, ArcGIS.com

1878 historical map overlay and GeoNB data for St. Andrews NB, ArcGIS.com

One of the groundtruthing groups was led by Dr. Matthew Hatvany, a marshland historian from Université Laval. Matthew was able to show workshop participants the marsh as it appeared on his handheld GPS device, and those carrying paper maps and smartphones with the ESRI ArcGIS app could compare their surroundings to features on the historical maps.

The St. Andrews mapping exercise worked well for a large group with no access to GIS software, but developing a web map like GeoNB is a massive project and likely out of the question for individual researchers and teachers. Having a provincial agency tailor its web map to suit your needs is not always an option for researchers, and although we were fortunate to have received this help, the overlays were only hosted on the GeoNB and ArcGIS.com websites temporarily.

Another solution for teachers who want to display a historical web map for a longer period is to tile the maps and host them on a course or personal website. One of the best ways to do this is through an open source program called MapTiler, an application that converts georeferenced rasters to a directory of tiled images for online publishing. The program is designed to overlay each map over Google Maps, Google Earth, or Open Layers, and these can be explored locally on a single computer or published on a public website. You simply input the raster, the spatial reference system, and a title for the new map and MapTiler generates the html file and supporting data for your website. You will need to include a free and unique API for each web map, which MapTiler explains and then integrates into the html automatically.

In another environmental history field trip to Malpeque Bay, a Prince Edward Island wetland of international significance according to a Ramsar-designation, I wanted to show students the first detailed map of the bay’s complex hydrology and coastal features. Captain George Bayfield surveyed the bay in 1845, and students can see the large map on the wall of the UPEI library and in digital form on the Island Imagined website. Both of these media are static and do not show the map in relation to the real world. Since both the built and natural environments have changed dramatically since 1845, we wanted to show students an overlay that let them compare coastal features and land use change over time. We could explore the map from the comfort of the classroom using Google Earth by generating a KML file with MapTiler. This allowed the usual pan-and-zoom navigation within Google Earth and set the map in the 3D display that students are now quite familiar with.

George Bayfield’s 1845 map of Malpeque Bay, showing a geotagged photo from Panoramio as an example of dynamic material from Google Earth’s public layers

George Bayfield’s 1845 map of Malpeque Bay, showing a geotagged photo from Panoramio as an example of dynamic material from Google Earth’s public layers

By setting the transparency of the Bayfield overlay we could see that the ecologically sensitive barrier islands along the north shore had changed considerably since 1845. In one dramatic change, the wind and tides reclaimed a 24-foot deep channel and replaced it with the surrounding sand dune ecosystem of Hog Island. The overlay made these landscape changes visible and dynamic, and students could quickly put it in the context of the Mi’Kmaq presence on the barrier islands, the fishing, farming, and tourism industries that developed along these shores, and the modern-day debates over dredging a deeper passage into the bay around Hog Island.

Transparent overlay showing the former channel and sand dunes on what is now Hog Island

Transparent overlay showing the former channel and sand dunes on what is now Hog Island

MapTiler’s other strength is the ability to generate basic web maps for publishing on the web, In the early twentieth century, Canadian cartographers combined aerial photo interpretation with surveys and field observations to plot what became known in 1927 as the National Topographic System (NTS). The NTS maps are an important source for environmental historians as they identified features in the built environment such as roads, dams, residential, community, and industrial buildings, and they also offer a view of the natural environment including features such as surface hydrology, wetlands, coastlines, and a basic breakdown of forest cover types. The most detailed NTS maps were called “one mile maps” because of their scale of one inch to one mile. The maps are large and fragile, and at this scale the paper maps of Prince Edward Island would cover a desk almost 3 meters long and 2 meters wide. Viewing these documents in a Google mashup allows historians to identify patterns in land cover and land use change, and often they reveal the origins of disturbances ranging from deforestation and stream siltation to brown fields or other residual forms of pollution.

The “one mile” maps were particularly useful for a field trip I led to the Acadian forest along the Newtown River in Eastern Prince Edward Island. After selecting an area which would show good examples of different land use and woodlot management practices (including both healthy and highly disturbed forests), the class examined the NTS maps for clues to the region’s early twentieth century environmental history. These maps are not yet available on government websites or local libraries, but the University of Toronto Map Library scanned some for the GeoWATCH project and then hosted the web maps that I georeferenced and tiled using MapTiler. Once the files are tiled and ready to be uploaded to a web site, they include two html files (one for Google Maps, the other for Open Layers) and a series of folders containing the image files for each viewing scale in the Google mashup. The html link to the map itself will open a Google Maps or Open Layers map window with navigation tools, a transparency slider, and a variety of basemap options (Map, Satellite, and Terrain). If MapTiler is instructed to create KML files for Google Earth, then it will also show a button called “Earth” which switches the window into the 3D Google Earth viewing mode.

josh1e

There are pros and cons to each type of web mapping. Professionally prepared web maps can be very expensive to create and maintain, but the advantage of uploading data to a professional web map is that it can accommodate many customized options. Building a Google mashup with a lightweight program like MapTiler is free and simple, and it can be published on a personal website as html. If presenting the map locally in Google Earth, it is possible to combine multiple historical maps as layers, but if publishing maps online on Google Maps, the software currently allows only one overlay per map.

josh1fSome GeoWatch web map examples:

Follow these links to see some early National Topographic Series maps prepared by Josh MacFadyen and hosted on the University of Toronto Map Library website courtesy of Marcel Fortin. The maps are overlaid on a Google web map. Viewers can adjust the transparency with the slider bar on the top right, view the historical map as an overlay on terrain or satellite images, or click “Earth” to switch into Google Earth mode and see 3D elevation and modern buildings (in Halifax and Dartmouth). Note: these historical images are large and will appear on the screen slowly, especially as you zoom into the Google map.

National Topographic System Maps – Halifax, 1920s
National Topographic System Maps – Western PEI, 1939-1944 
National Topographic System Maps – Eastern PEI, 1939-1944

 

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I am an Assistant Professor of Environmental Humanities in the School of Historical, Philosophical, and Religious Studies and the School of Sustainability at Arizona State University. As co-investigator on the Sustainable Farm Systems Project (based at the University of Saskatchewan) I am building on the work of the Great Plains Population and Environment Project, conducting new research in agriculture on the Plains and my own case study of Prince Edward Island. From 2010-2014 I was a SSHRC postdoctoral fellow and then NiCHE project coordinator.

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