Using high-precision aerial imagery to map cities

Government agencies are increasingly turning to high-precision aerial imagery to solve city-planning conundrums. Three recent case studies show how emergency 9-1-1 services gather data to provide updated maps to emergency services to get to the right locations as soon as possible; reveal how a city’s public works department streamlines data collection for more efficient infrastructure management; and how to give GIS professionals instant access to the most current information available — all in the cloud.

Photo: Nearmap

It’s said a picture is worth a thousand words. In the case of aerial imagery, where location data is packed into every pixel, a picture could save lives.

Emergency dispatch is just one type of government agency now relying on high-quality aerial imagery. With up-to-date georeferenced imagery of their own towns and counties, agencies are not only improving response to emergency calls, but also streamlining public works and enhancing city planning.

A company providing that imagery is Nearmap, which serves more than 8,200 organizations and businesses globally using small aircraft for image capture. The aerial mapping company provides high-quality imagery as a subscription service delivered through the cloud. Its photo maps are taken at least twice a year, with leaves both on and off the trees, to provide different views of locations in different seasons.

Nearmap’s patented camera system and software pipeline enables it to capture aerial photos, stitch them together into seamless digital maps, and publish the content online within days of capture. Above, Nike’s headquarters in Portland. (Photo: Nearmap)

Aircraft offers a huge advantage over unmanned aerial vehicle (UAV) or satellite imagery. Airplanes can cover much greater distances than UAVs, and pilots pay heed to the weather and fly below cloud layers to deliver the clearest visuals possible. Unlike space-based platforms, airplanes operate at lower altitudes, also increasing the resolution, and can fly on demand, unlike satellites that have set orbits dictating their periodicity for returning to a target area.

Nearmap’s powerful, patented technology allows it to deliver high-resolution aerial imagery as a service: orthographic (straight down) maps, multi-perspective panoramas and oblique aerial views — all at resolutions four times clearer than free satellite imagery.

Once photographed, the images are stitched together in the cloud in a matter of days, where they are available for viewing and analysis on desktop, tablet and mobile devices via a subscription service.

Nearmap’s proactive capture model is based on population — the larger the population, the more captures it takes per year. Nearmap images 88% of Australia’s population, 70% of the U.S. population, and 75% of the New Zealand population.

Nearmap captures many areas multiple times throughout the year; for many locations this gives customers a leaf-off and leaf-on view. Providing spring leaf-off captures allows customers a view of the ground that is typically obstructed by foliage the rest of the year.

The flight plans cover approximately 430 urban areas that are flown, captured and processed, and then served up via the MapBrowser in-browser tool, or supplied via application programming interface (API) for use in various design platforms. When a user subscribes to Nearmap, the capture is immediately available with any and all historical captures, without the need to pay for a dedicated flight.

“To capture imagery for a map, a plane has to crisscross over its own flightpath. Each sweep has to overlap the previous by approximately 70%,” explained William Tewelow, GPS World’s contributing editor for geointelligence. “Vertical (or nadir) is straight overhead. Oblique is everything else, but usually not exceeding 30% to either side because it distorts the structures and vertical features (parallax), makes mosaicking difficult, and shadows structures behind other structures.”

That said, oblique imagery is important for building 3D meshes for imagery point clouds, Tewelow said, as well as seeing various angles of a structure.

Following are examples of the creative — and surprising — ways government agencies are using Nearmap imagery to improve their services today, and prepare for future changes in their communities.

Better 9-1-1 address mapping

Shelby County is the largest county in Tennessee in both population (927,644) and geographic area (785 square miles). Memphis is the county seat, home to the county’s Emergency Communications District, for the operations of the local 9-1-1 emergency system.

The district provides Shelby County residents with an efficient emergency telephone number service using the latest technology, equipment and training for the various emergency service providers and dispatch centers.

For each dispatch center, the district provides county address location mapping. A secure database known as an ALI (Automatic Location Identification) contains the exact 9-1-1 address for any given associated phone numbers.

Albany, N.Y.: A house fire in progress. (Photo: Nearmap)

When a 9-1-1 call comes in, the database is queried by the Public Safety Answering Point to obtain the caller’s location. This data is then placed in the computer-aided dispatch software and 9-1-1 mapping software used by the district to help fire and rescue, emergency medical services and law enforcement gain instant access to updated maps containing GIS data needed to get to the right locations as soon as possible.

The 9-1-1 mapping system uses geodetic coordinates to plot wireless calls on the map. The system also reverse geocodes the coordinates to provide the 9-1-1 telecommunicator with a calculated civic address based on proximity of other features in the map, such as address points or streets.

Out-of-Date Imagery. For years, Shelby County’s aerial image process required a contracted flight to photograph the county areas. Because of the high cost of capturing those images, the county purchased images once every two years, after pooling resources from various county entities.

“We had gaps where we wouldn’t have updated imagery,” said Timothy Zimmer, the district’s GIS administrator. “While the images were high resolution, there were issues with mosaicking the separate images together, and since the imagery was taken every two years, many rural and unincorporated areas were out of date.”

With out-of-date images, the county had to develop alternate methods to locate addresses for the 9-1-1 systems.

Moving into the Cloud. In the summer of 2018, Zimmer began to work with Nearmap. With Nearmap, Zimmer and his team can access current imagery to geocode new addresses and developments as well as plot new roads into the 9-1-1 mapping systems (Figure 1).

Figure 1: Mapping image for Shelby County’s 9-1-1 system. (Photo: Nearmap)

For Zimmer, the biggest advantage is that Nearmap’s imagery integrates directly into Esri’s ArcMap, ArcPro and ArcGIS Online applications, so he can overlay GIS information directly over the high-resolution imagery.

“I really like how Nearmap is integrated into the GIS stack,” Zimmer said. “We’re able to stay on top of new developments, roads, and addresses. Being able to have Nearmap imagery integrated into our GIS systems helps us be much more accurate.”

The combined impact of data services, base maps, Nearmap imagery and third-party data are improving all aspects of public safety, including law enforcement, fire and emergency medical services.

Other Shelby County agencies also are using the district’s imagery and GIS data. “The county clerk and the utility company are using our address mapping data because Nearmap has helped enable us to be much more current,” Zimmer said.

Public works in a fast-growing city

Durham is one of the points in North Carolina’s high-tech Research Triangle and home to Duke University.

An economic and cultural renaissance is happening in the city. With a revitalization of its downtown district, the redevelopment and repurposing of former tobacco districts into tech hubs, and chic loft-style apartment complexes, Durham is rapidly growing beyond its most recently reported 250,000 population numbers.

Impervious Challenge. In early 2018, the city’s growth explosion prompted Edward Cherry, GIS administrator for the City of Durham Public Works Department, and his staff of 14 GIS professionals to seek ways to streamline their data collection.

The department manages all infrastructure data for the city, including mapping the impervious area. As defined by the U.S. Geological Survey, impervious surfaces include highways, streets, pavement, driveways and even house roofs — any surface that won’t absorb rainwater. Rather, the rain runs off into storm sewers and then into local creeks; localized flooding is often the result.

Durham Public Works manages half a billion square feet of impervious area. The city’s $16 million-a-year Stormwater Utility Fee income was a driver for Cherry’s team to explore satellite imagery options. Imagery from satellites, however, were infrequent and too low-resolution to meet their needs. The satellites captured images only once-a-year, and that might be on a cloudy or rainy day. Clouds cast shadows, and rain makes pavement appear newer than it is.

Nearmap’s aerial imagery, captured in Durham three times a year at a 2.8-inch ground sample distance (GSD), solved the problem (the GSD of each individual pixel in the imagery represents 2.8 inches on the ground. See Figure 2).

Figure 2: Rapid growth requires frequent imagery. Above is a new Durham neighborhood under construction. (Photo: Nearmap)

Dozens of projects in the Public Works Department — from road maintenance and pothole patching to water sampling and degradation — are using the improved imagery, which has saved the city money, reduced time spent in the field, and allowed crews to use real-time imagery when they are working in the field.

Monitoring Pavement Conditions. The City of Durham is responsible for maintaining most of its roads, and conducts a road-condition survey that samples different sites, evaluating the level of degradation.

Since 2014, Nearmap has regularly captured Durham streets at the same resolution and accuracy, and both the historical and current data are available to the department. With multiple high-quality image captures at high resolution, surveyors can see sections that have been recently paved. “We don’t need to send crews out to an area where a stretch has already been paved,” Cherry explained.

Road Repair Documentation. As in any city, the patching of potholes is an ongoing project for Durham’s public works department. With imagery, the city has been able to streamline the process.

Traditionally, the streets department sent out inspectors to spray paint and circle areas that required repairs. “Then we would produce maps and hard copies to direct [road repair contractors] ahead of time on a scheduled event,” Cherry said.

Now the city uses an application integrated with Nearmap imagery by which contractors can view the job on their smartphone or tablet while in the field. The surveyors can edit and draw the areas that need patching instead of physically going out and spray-painting them. “Then, in real time, the people doing the patching can see a very high-resolution image of where they need to do the work,” he said.

The pothole image captures are recorded, so the city knows where and how many potholes were patched. “We can see where work has been done when we are billed for it,” Cherry said. “We can visualize the work, which is an added bonus.”

Mapping Riparian Zones. With imagery previously taken only when the leaves had fallen (known as leaf-off), surveys of riparian zones in Durham proved limiting.

With imagery captured during both leaf-off and leaf-on seasons, riparian buffers around streams can be properly monitored for expansion. The buffers can be altered if there are issues with a stream’s path, such as sediment clogging the flow, repeated flooding or people intruding on a buffer.

Change Detection. High-resolution imagery has improved Durham’s billing process by producing web service maps that capture individual storylines. Stormwater billing customers, for instance, can visualize their properties with the impervious areas mapped out and tied to their billing records.

With up-to-date imagery providing data for change detection software, records also show when a customer has added a driveway or an extension to their house.

Figure 3: Aerial Imagery of an Apex neighborhood displayed in ArcGIS from Esri. (Image: Nearmap)

“Having access to imagery back to 2014, we’re able to go back in time during the thrust of development and monitor it forward,” Cherry said.
Nearmaps’ library of historical imagery allows for change detection algorithms to run in Esri’s ArcGIS imagery analysis software suite.

More efficient government

GIS data combined with aerial imagery is tailor-made for city planning and managing urban growth.

For instance, the population of Apex, N.C., has more than doubled since 2000. Situated near Raleigh and the state’s Research Triangle Park, Apex was rated number one in Money magazine’s 2015 “Best Places to Live,” which cited Apex’s charming downtown, highly rated schools and high-paying technology jobs.

Figure 4: The post-construction image of the same neighborhood is much more accurate. (Image: Nearmap)

To manage the explosion in development, Apex’s GIS professionals needed instant access to current information. The old-school method required planners to drive the streets, inspect roadways, and roll out the measurement wheel. Now, the combination of Esri ArcGIS for mapping and Nearmap high-resolution aerial imagery allows them to visualize and measure within six inches of accuracy.

“Our ability to leverage our GIS operation improved dramatically with Nearmap. The flexibility of its cloud solution and ability to integrate with ArcGIS has redefined how we rapidly respond to staff and citizen requests,” said Steve Nelson, a GIS professional with Apex.

The use cases for these solutions are diverse. Law enforcement calls on GIS professionals from Apex to quickly provide current, clear, aerial photography for active or ongoing investigations. Planners focused on development are charged with meeting state regulatory reporting guidelines when it comes to building and maintaining roads. Environmentalists want to know if anyone is digging on protected land.

Figure 5: Measuring for reimbursement in Apex. (Image: Nearmap)

For the State Street-Aid Program, financial allocations are made to incorporated municipalities eligible under North Carolina law. State routes that pass through incorporated cities are maintained by the cities. Cities are responsible for paving new roads, but the state has the power and economic means to reimburse them.

To qualify for reimbursement for new roads developed and maintained, Apex needs to submit a report to state engineers for review. The report documents the distance for all newly paved roads.

Before the new system was in place, GIS professionals had access to imagery from 2013, but the actual development took place after this. In (Figure 3), the 2013 imagery simply outlines the parcels and rights of way. It has no detail with respect to where the roads start and end, so a lot of field work was needed to take measurements, drive roads scattered across the county, and collect data.

Figure 6: Green lines indicate new streets in Apex in a single year (2013). (Image: Nearmap)

With the new system, workers have instant access from their desktop to the same location as it currently is. They can see exactly where the edge of the road starts and stops (Figures 4 and 5), which is different from the yellow-lined “right of way” depicted in Figure 3. While in the office, GIS professionals can measure distances precisely, creating an accurate representation of ground truth.

Figure 6 highlights a small portion of new roads built in Apex in one year. The green lines highlighted are scattered across the city. As Apex continues to grow and annex adjacent territory, the dynamic nature of the growth will be captured and uploaded to the cloud.

Unlocking Potential

As cities grow in complexity, mapping becomes integral to planning. With the advances aerial imagery provides, cities are starting to unlock the full potential of location data and visualizing a better future.

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