Polk County highlights public LIDAR viewer, says data aims to speed planning and conservation

Polk County planning staff and consultant Adam Derringer of Ayers and Associates demonstrated a publicly accessible online LIDAR viewer that county officials said will make high‑resolution elevation data easier to use for planning, conservation and infrastructure work.

County staff said the LIDAR was collected in spring 2022 in coordination with the U.S. Geological Survey’s 3D Elevation Program and that Ayers built the web viewer to allow staff and residents to access the large dataset without specialized software.

The viewer streams the county’s point cloud and derived products in a browser. Adam Derringer, a consultant with Ayers and Associates, demonstrated measurement and analysis tools, showed 1‑foot contours, a searchable parcel overlay and a culvert layer he said contains roughly 23,695 mapped culverts countywide. “This dataset is measurable,” Derringer said, demonstrating line and area measurements and an elevation profile across steep terrain.

Why it matters: staff said the viewer will let departments and the public examine slope, depressions and drainage features quickly without having to process terabytes of raw LIDAR files. Officials said that could speed site assessments, culvert sizing, conservation planning and pre‑field checks for staff and consultants.

What the viewer contains and how it works: the presentation showed a colorized point cloud (color taken from aerial imagery), a digital elevation model (DEM) usable for measurements, one‑foot contours, culvert lines and a set of derived “closed depressions” (basins). Derringer showed tools for measuring elevation differences, creating elevation profiles, estimating depression area and depth, and running flow‑accumulation visualizations in other counties. He noted the viewer streams multiple terabytes of data from the cloud and is designed to run in a standard web browser without GIS or CAD software.

Accuracy and limits: Derringer said the Polk County project was flown to meet USGS Quality Level 2 (QL2) standards, designed for about two points per square meter. “On a hard surface, the data was designed to have 10 centimeter accuracy (RMSZ),” he said, adding that vertical accuracy tends to degrade in vegetated or wet areas. He also flagged a key limitation: LIDAR does not reliably penetrate liquid water, so ponds, lakes and full manure pits will not return ground points beneath the water surface and will appear hydro‑flattened in the DEM.

Examples and county uses: Derringer demonstrated measuring tree and building heights, checking ski‑hill vertical drop, identifying sinkholes and estimating the acreage and maximum depth of closed depressions (examples cited: a 1.2‑acre depression and a 4.4‑foot maximum depth). He showed that flow accumulation and watershed delineations can be used to estimate how much acreage may drain to a culvert — an example noted roughly 3,000 acres draining through a single culvert in one location.

Access and distribution: staff said the viewer is live on Polk County’s GIS site in the same area as the parcel and aerial imagery viewers and requires no login. The county and Ayers plan to use the viewer for staff training and public access. Derringer said the USGS allows grant applications to re‑fly areas roughly every five to eight years; counties typically plan updates on a five‑ to ten‑year cadence depending on change rates and available funding.

County staff and the consultant encouraged users to consult the vertical accuracy report included with the project for site‑specific checks before using the data for engineering decisions. The committee recorded the demonstration and asked staff to make the viewer training resources available to other departments.