Viewshed analysis: what can you see from your property?

Who uses this

• Buyers. Check the view a site really has, and whether it is at risk.
• Planners and architects. Assess the visibility of a proposed building from roads and neighbors.
• Radio and security installers. Site a repeater, a camera or a wireless link.

When to use it

• Checking what a house site, a deck or a lookout will see, and what will see it.
• Siting a camera, a radio repeater, a wireless link or a security light.
• Assessing whether a proposed building will be visible from a road or a neighbor.

Tools for your job

Viewshed is one step in a bigger question. These are the jobs it helps with, and the tools that go with it.

How to use it

1. Open Viewshed and click the observer point.
2. Set the eye height above ground, the target height (0 for the ground itself, or the height of a thing you want to see) and the range.
3. Choose bare ground, or the surface model so trees and buildings block the view.
4. Run. Visible ground is highlighted; hidden ground is left clear.
5. Download the visibility grid as a GeoTIFF for GIS. Downloading needs a pass.

Step by step: Devils Lake

We check what can be seen from a point on the East Bluff above Devils Lake, standing at eye height.

1.Open Viewshed, choose how far to look and the eye height (standing), and click the observer point.

2.Green ground is in line of sight. The panel gives the share and area of the ground within range that is visible. The bluffs hide the ground behind them.

What it showed

• To see where a new house would be visible from, put the point on the house and set the eye height to the roof ridge.
• In Brown County, choose terrain, trees and buildings so the county’s surface model blocks the view too. Elsewhere the view is over bare ground, so trees and buildings do not block it.

How it works

From the observer, rays are cast across the terrain in every direction. Along each ray the tool tracks the steepest angle seen so far; any cell that falls below that angle is hidden behind something nearer. The earth’s curvature and standard atmospheric refraction lower distant ground slightly, as they do in reality.

Reading the results

Visible means a straight line exists from the eye to that cell at the target height. It says nothing about how clearly, or whether haze or a window frame intervenes.

Raise the target height to answer “can I see a two-story house there” rather than “can I see the ground”.

Limits and caveats

• Range up to 5 miles. Distant views beyond that are not tested; Views beyond the chosen radius are out of range.
• With bare ground, trees and buildings do not block the view. With the surface model they do, but only as they stood when the lidar was flown.
• The optional surface model covers Brown County only. Outside usable Brown County data, Sunlight, Viewshed and Sightline fall back to bare earth, so trees and buildings do not count. Object Heights needs usable surface data. Its source date can differ from the 3DEP ground model.

Data and attribution

Results come from the USGS 3D Elevation Program (3DEP) bare-earth elevation model: lidar at 3.3 ft per pixel where it has been flown, with older lidar at about 9.8 ft per pixel and coarser sources at about 33 ft per pixel elsewhere, with elevations above NAVD 88. The optional surface model is limited to Brown County. Outside usable regional data, Sunlight, Viewshed and Sightline fall back to bare earth; Object Heights needs usable surface data. Surface and ground source dates can differ.

USGS 3DEP elevation data and USGS maps are U.S. Government works in the public domain: you may use the results, including commercially. A credit to the USGS 3D Elevation Program is appreciated, and every file you download carries it. Wisconsin parcel boundaries are aggregated local-government data, not legal surveys; the parcel disclaimer accompanies the selection. Brown County surface data is credited separately when used. The Esri aerial basemap follows Esri’s terms and is display-only; downloadable aerial photos use USGS NAIP.

Questions

Related

Related tools

• Sightline — Checks whether one point is visible from another, and if not, where the view is first blocked and by how much.
• Sunlight — Models hours of direct sun across a site on any day of the year, with shadows from terrain up to 1.86 mi away and, where Brown County’s regional surface model has usable data, from trees and buildings.
• Object Heights — Estimates the height of buildings and vegetation above the ground by subtracting the USGS 3DEP bare-earth model from Brown County’s regional surface model.