Prince William County's Geographic Information Systems Office gathers its aerial imagery by contracting pilots to fly over the county every two years and take pictures of the ground. The photos are then used in conjunction with overlays, or layers, that show parcel boundaries, street addresses, and past and present building locations, among other things.
Before 1998, customers could only see the imagery as hard copy photographic prints. After 1998, digital began to take over and aerial photographs with layers to accompany them came into use. The Geographic Information Systems, or GIS, office also started to incorporate the digital photographs and layers into its web mapping applications, said GIS Systems Developer Chris Watt.
Access to the digital imagery allows people to find out where things used to be, help answer zoning ordinance questions, determine changes in land use and research the history of the county, Watt said.
Digitizing the prints and stitching them together makes it easier to pinpoint a location. It is hard to find a particular spot in a group of individual photographic prints. "Traditionally, people have had to come in and leaf through all of the images to try and find what they're looking for, and now they can search online. They don't have to look through a stack of images for different years. Now they can just click through the different layers, and they'll appear once they found the area of interest," Watt said.
Until recently, some of the older aerial photos have not been available in digital format, which meant that GIS customers had to do their research during office hours. Additionally, the aging prints were showing significant wear and tear. The corners of the photographs were rolling, and the photographs showed creasing, cracking and bending.
Digitally capturing the old print data so that it can be seen online anytime on the GIS website will prevent further degradation and allow the public to easily access the information. "To provide better access to the citizens and to the county employees, we wanted to make them available digitally and incorporate them into the existing web applications. It's convenient. They can now do this at home or at their desks," Watt said.
Except for photographs gathered in 1937, image collection prior to 1954 was sporadic and will not be included in the project, Watt said. In coming months the GIS office will add layers from 1990, 1991 and 1995. The most recent years to be digitized were 1954, 1979 and 1987. Images from between 1956 and 1997 will be added as the project continues.