E-Mail This Article to a Friend Map quest Carolyn Bennett and the Boston Redevelopment Authority’s Office of Digital Cartography and Geographic Information Systems show Bostonians where it’s all at BY TAMARA WIEDER

IF YOU’VE TRIED to navigate Boston’s streets during the course of the Big Dig, you’ve likely been frustrated, confounded, and just plain lost on more than a few occasions. Keeping track of the myriad changes to the city has been, for many of us, a lesson in futility.

Not for those in the Boston Redevelopment Authority’s Office of Digital Cartography and GIS (Geographic Information Systems). Because the department provides mapping support for a host of city agencies, it’s the job of manager Carolyn Bennett and her office’s cartographer and GIS specialist to update the city’s geographic data whenever changes small or large — a realigned street, a road moved underground — occur. Need a zoning map? Bennett’s department is responsible for those, too. Want to see the changes, over time, to a particular area — or just want to see what your block looks like from above? You’ve come to the right place.

Q: Tell me what the Office of Digital Cartography and GIS does.

A: [We’re] part of the citywide planning department here, with the BRA. We are here to provide mapping support for the BRA staff. That’s a priority. And then we also provide mapping support to other city agencies as well. We have different programs within the BRA — transportation, citywide planning, community planning, zoning — and we provide any type of mapping analysis that is needed for the planning staff to do their job. Most of the time our mapping is related to certain projects that are coming to the BRA for project review. Planners will need a lot of background information — existing conditions, where the site is, what the proposal is, the surrounding buildings, and all type of street information that might be available — to help them make their decisions. We have a bunch of base data that we use to do our mapping with, base data that the city has provided from its various agencies, which also use GIS.

Q: Give me an example of what that data might be.

A: The real typical GIS is planimetric data; planimetric data is data that you can see that’s on the ground, like streets, sidewalks, hydrography — you know, you can see water, you can see streams, you can see ground cover. Within a city environment, the lampposts and pretty much everything that is the built environment that you can see from an aerial photograph is considered planimetric data. That’s the base data. The building footprint, that would be part of a planimetric base map. Then the city block is a big one, too. The sidewalks, the bridges — all of the infrastructure. So a city will have developed pretty good base mapping; the scale is typically one inch to 100 feet. This data is used by almost every agency within the city to do all sorts of mapping. They do data management with it, they do spatial analysis with it, and you can overlay other information, like land use or zoning. You can use census information; the Census Bureau has divided the different geography, so you have census tracts and block groups, and then you have demographic and socioeconomic information for each block group, so that can be mapped, and you can do analysis based on demographics and income levels and that sort of thing. [You can look at] school-aged children, to find out what growth has been occurring and where, and where a municipality may have to build another school. So all of these things work together.

Q: How do you define GIS?

A: It can be defined as an collection of computer hardware, software, geographic data, and staff, designed to capture, store, update, manipulate, analyze, and map all forms of geographically referenced information. GIS can be linked to information relating to economic development, planning and zoning, environmental monitoring, law enforcement, and property management, to name just a few.

Q: How has the Big Dig affected the role of your department?

A: The only thing that’s changed is, our data layers [need] to be updated. [If] a street has been realigned, and it’s now underground, what we have to do is make sure that our maps appropriately display the new road alignment.

Q: It seems like those kinds of things are changing almost daily.

A: Right. There are new building footprints that either come or go. There are streets that may be reconfigured or realigned, and then we have to make sure that we update our data layers to make sure we have the appropriate information available for people when we do our maps. So there’s not only the day-to-day mapping and creating maps for staff, but there’s also the data updating. Because our maps are only as good as the data that we put on them.