‘X’ marks the spots

Large white ‘Xs’ on county roads aid aerial photo survey

This weather-damaged plastic “X” is at the Osgood Avenue-Minnesota 36 intersection across the frontage road from the Holiday station in Oak Park Heights. The marker will remain there until aerial photos recently taken of the county are approved for accuracy, then will be removed. Markers painted on roads are allowed to fade over time. (Gazette staff photo by Erik Sandin)

This weather-damaged plastic “X” is at the Osgood Avenue-Minnesota 36 intersection across the frontage road from the Holiday station in Oak Park Heights. The marker will remain there until aerial photos recently taken of the county are approved for accuracy, then will be removed. Markers painted on roads are allowed to fade over time. (Gazette staff photo by Erik Sandin)

A number of large white “Xs” popped up like giant mushrooms along Washington County roads last week.

The markers — some painted on roads, others placed on roadsides — served as “targets” at strategic locations countywide prior for a new set of aerial photos taken of the county last weekend.

The county hires a company to take aerial photos every few years; with the last set of photos taken in 2009, said County Surveyor Michael Welling.

The photos are used for the county’s geographic information system (GIS) maps. County employees use GIS maps for a range of work, including staff from the public health department, the assessor’s office, county engineer, county sheriff and attorney’s offices, GIS Support Unit and others. In addition, private individuals such as developers, real estate agents, planners, surveyors or “anyone who is doing any kind of development of land,” can pay to get access to the maps, Welling said.

“The photos are much more accurate than the ones available” on popular websites, Welling said. Part of that has to do with the Xs. They are “targets” placed at known survey points that can be seen on the aerial photos and are used to adjust the photography, increase accuracy and create more accurate maps.

Plans called for the contractor’s plane to fly last Friday, because there is a narrow timeframe of opportunity to shoot the aerial photos. It has to be done after ice out and snow melt, but before trees grow out their leaves.

“This year has been particularly challenging,” said project manager John Baer. When taking the aerial photos, the plane flies along north-south flight lines over the county, photographing mile-wide swaths, then turning at the end of each trip to provide some overlap at the county’s bordering rivers and counties to get a full sweep of the county. Including the county and overlap areas along the borders, total area photographed is about 500 square miles.

“I did get notice from the vendor that they did complete aerial photos over the weekend,” Baer said.

This year’s competitively bid project costs $37,500, down from the 2009 price of $66,000.

Once completed, the photos are reviewed by Baer to ensure accuracy, before they are ready for use by Oct. 1.

Once the photos are cleared, the plastic “targets” will be picked up from their marking places in the county. Targets painted in roads will be allowed to fade over time.

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