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: Mount Hood

We check what can be seen from a point near Timberline Lodge, 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. Ridges on either side hide the canyons beyond 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.
• Choose terrain, trees and buildings so DOGAMI’s surface model blocks the view too.

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; Mount Hood from Portland is 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 surface model is DOGAMI’s statewide mosaic, which is still being completed. Where it is empty the tool falls back to bare earth, so trees and buildings there do not count.

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, and the 1/3 arc-second model, about 33 ft per pixel, elsewhere, with elevations above NAVD 88. The tools with a surface option (Sunlight, Viewshed, Sightline, Object Heights) read DOGAMI’s statewide digital surface model of trees and buildings.

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. DOGAMI lidar products are published by the State of Oregon; credit "DOGAMI / Oregon Lidar Consortium". County taxlot boundaries are the assessor's GIS data, not surveys, and each county publishes its own disclaimer, shown with the parcel. The aerial basemap is from Esri and follows Esri's terms; it is not included in downloads.

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 DOGAMI’s surface model exists, 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 DOGAMI’s lidar surface model.