UW Map Library Offers Online Access to Historical Air Photos of the Region of
Waterloo
Eva Dodsworth, BA, MLIS
Eva Dodsworth is the Geospatial Data Services Librarian at the University of Waterloo Map
Library. edodswor@library.uwaterloo.ca
Digital Historical Air Photo Project
http://www.lib.uwaterloo.ca/locations/umd/project/index.html
The University of Waterloo Map Library is a cartographic and GIS resource centre to academics,
community organizations and interested members of the local community. With a collection of
over 100,000 maps, 49,000 air photos and being the campus’ hub for geospatial data, the
library is frequented by many user groups and individuals – serving a variety of interests and
purposes. Until most recently, many of these users were able to only access the collection in
person, during library hours. Now, one of the library’s most popular paper collection, the
historical aerial photographs, have become available online for users to view and download
from their home and business computers.
The Map Library’s air photo collection includes stereoscopic images of the Region of Waterloo
taken as early as 1930 to as recent as 1995. The air photos are widely used by students,
business contractors, history buffs and home owners who like to study the air photos for land
cover, property information, feature identification and changes in these over time. With many
users physically handling the photos, photocopying them and/or scanning them, library staff
felt it was necessary to implement a preservation plan for the older images.
Archiving Air Photos
The library’s earliest photos consist of 670 images flown in 1930 and 550 images flown in the
1940s. The library commenced the project using images from these years and in the future will
consider archiving photos from the 1950s and continue on with years that are free of copyright.
(note to editor: sidebar 1). With approximately 1200 photos to work with, it was decided that
the best archival process would be to scan each photo at high resolution (600 dpi, Tiff imagery)
and store on multiple DVDs. This archival and storage procedure provides the library with an
electronic duplicate in case any of the original photos are misplaced or damaged. In order to
reduce the amount of handling of the original photos, the library needed to provide users with
easy access to the electronic images. Offering the images on the internet deemed to be the
most convenient and user-friendly way to view and access the imagery.
Providing Online Access to Photos
Selecting an Online Interface
With so many imaging technologies and World Wide Web applications available, the library
struggled with the decision with the type of image viewing and downloading interface to use.
Using cutting edge technology to enable interactive mapping such as map zoom-ability, image
mosaicking and specific air photo feature search-ability were very attractive options. Offering
users the ability to overlay current streets as well as historical streets (as they were in 1930),
over the images to aid in distinguishing location and landscape features would be tremendously
beneficial as well. The library also had to consider the number of images to upload to the
server and the effects large size images would have on the users. Would users prefer smaller
images with lower resolution, or larger size images with no resolution loss, for example? And
which image formats should be made available? Although there were many attractive
possibilities and several different options obtainable, the library opted to go for an in-house
website with a simple but effective image organizational structure. The library’s primary goal
was to create an online development that provided users with easy access to historical
coverage of the Region of Waterloo.
Finding and Accessing the Photos
The goal of the online project wasn’t to provide users with electronic copies of the air photos,
but rather to provide them with historical coverage of the Region of Waterloo. The difference
between these two is that the latter focuses on leading the user to historical images of the
geographical area of interest, as opposed to a specific photo defined by an air photo flight line
index. (editor – insert sidebar 2). With the flight line index as the only pathfinder, users often
spend great effort correctly identifying the photo of interest. When photos do not have any
distinguishing features on them, errors in interpretation can easily be made – for example,
users may believe they are looking at an image of their grandparents’ farm when in fact they
are looking at their neighbours’ across the way. Misinterpretation commonly occurs when
working with landscape that has changed dramatically over so many decades. Historical
photos can therefore be unidentifiable - and using clues that one is familiar with, such as
current streets and rivers, will assist the researcher in finding the exact area he/she is looking
for.
Library staff created an online index that accurately leads the user to their photo of interest.
The index is a clickable map that includes the Region’s boundaries, streets and township or city
names. See Figure 1. Clicking on the map opens a detailed street map of the city or township.
See Figure 2.
Figure 1 : A clickable index. Clicking on your area of interest brings up a larger map.
Figure 2 : The larger map with detailed street files.
This larger map is overlaid with a 2.5 x 2.5 square km grid. Each square, or tile, provides a
link to the historical image that encompasses that tile. When users click on any individual
grid tile, they will access air photos that have been stitched together and cropped to neatly
align within the 2.5 x 2.5 square km distance. In lieu of offering all of the 1200 scanned
images on the internet, and with many that overlap due to the attributes of stereoscopic
imagery (see figure 3), library staff created image tiles with the individual photos. (editor –
add sidebar 3)The tiles were created using anywhere between 1 to 3 air photos. All tiles
were made available in jpf, tiff and pdf image formats.
Figure 3. When the air photos are aligned correctly, there is a significant overlap. One
geographical area of interest may be represented in several air photos.
Offering Additional Navigational Aid : Georeferenced Imagery
A major goal for this project was to take it a step further and offer users the option to use the
images in a GIS program. A GIS program will place the image correctly on the earth’s surface.
Using GIS technology will help provide clues about the past - and as is the case with older
photographs, familiarity is the key to successful navigation. Since many internet users are
familiar with Google Earth, compatible Keyhole Markup Language (KML) files were created so
the users can view the images in the popular online mapping program. One of the advantages
of using a GIS program is that one can overlay streets on the historical image to accurately
interpret the photo’s location. Figure 5 shows a 1930 image of a farmland in Waterloo. On its
own, the photograph doesn’t tell much of a story, but once placed spatially correctly in Google
Earth (figure 6), the overlaid streets provide the information necessary to identify the location
as the University of Waterloo.
Figure 5- A georeferenced historical air photo overlaid in Google Earth’s current aerial
photography.
Figure 6 : Using Google Earth’s current streets to assist in interpreting the historical image.
The combination of aerial photography and georeferencing technology brings traditional air
photo interpretation to a higher level. With the GIS tools available, a user can compare the
past and the present with very close precision. If the user is interested in studying the loss of
forestry for example, one can overlay an historical aerial photograph over a more recent one to
study the changes and discover precisely where new trees have been planted.
To provide users with the added benefit of spatially referenced images, all original 1200 images
had to be georeferenced by staff. Georeferencing a photograph is the process of adding spatial
coordinates to the image so that it has a relation to the earth’s surface. This process was
completed in a GIS program and took anywhere between 3 minutes to 25 minutes for each
photo. By far, it was the most time consuming element of the entire project, as staff had to
study in detail all 1200 images and interpret any features present into order to accurately
assign latitude and longitude coordinates to those features. The most challenging component
was working with photos that represented geographical areas that have dramatically changed
over the past 80 years. Staff were comparing an 80 year old image to today’s streets and rivers
map, trying to find commonalities to define the location of the photo. Common markings used
are often street intersections, river bends and unique terrain patterns on farm land. See Figure
7. Figure 8 is an example of one of the more challenging photos from 1930 that required
intensive interpretation and orientation. When compared to a 2008 image of the same area
(figure 9), one can begin to appreciate some of the difficulties present in historical air photo
interpretation.
Once the staff member locates several points on the photo, the GIS program records the
coordinates of each point and tags the photo with a spatial reference system. This newly
georeferenced image can be added into a program that reads coordinate systems and will
correctly place that image and other features on a map.
Figure 7 : The shape of the road in this photo was used to identify its location.
Figure 8 – Due to the lack of recognizable features, the location of this photo was very difficult
to identify. When comparing this 1930 image to the 2008 image (figure 9), the location is even
harder to distinguish because the landscape has changed so much.
Figure 9
Conclusion
Aerial photography captures moments in time, offering a pictorial preservation of history. This
project offers convenient access to Kitchener-Waterloo’s local history, and offers users the
added value of combining the photos with GIS technology.
Sidebar 1
The term of copyright on aerial photographs published in Canada by federal and provincial
governments is 50 years after the first date of publication. Therefore, air photos published
prior to 1958 are in the public domain and may be freely copied.
Sidebar 2
An air photo flight line index is a map with aerial survey information printed on it. The location
of the photos, along with its roll and frame number is plotted on a topographic or street map.
The user requires the photo’s flight roll and frame number to retrieve the photo.
Sidebar 3
Stereoscopic imagery (3D viewing) is the result of overlap, which is the amount that one
photograph includes an area covered by a neighbouring photograph. There is approximately
60% forward overlap between photographs and 40% lateral (side) overlap.