Land records · Parcel maps · October 7, 2026
What Is an Orthophoto? Aerial Imagery for Maps
What is an orthophoto? An aerial photo corrected so scale is uniform and it lines up with maps. How counties use orthoimagery with parcel layers.
What is an orthophoto? An orthophoto, or orthoimage, is an aerial or satellite photograph that has been geometrically corrected so that it has a uniform scale and accurately lines up with maps. Regular aerial photos have distortions caused by camera tilt, lens effects, and terrain, which make objects appear in the wrong place. Orthorectification removes these distortions using elevation data and ground control points. The result can be used like a map, allowing accurate measurements and overlays of parcel lines, roads, and other GIS layers. This page is general land-records background, not legal advice.
Why orthorectification matters
| Problem in raw photos | Correction |
|---|---|
| Camera tilt | Adjusted using flight data |
| Terrain relief | Corrected with elevation models |
| Lens distortion | Removed with calibration |
| Scale variation | Made uniform |
Uses
- Base imagery in county GIS viewers.
- Measuring distances and areas.
- Checking improvements for assessment.
- Planning and engineering.
- Comparing changes over time.
See how to use a county GIS viewer.
Resolution
Orthophotos are described by pixel size, such as 6 inches or 1 foot per pixel. Higher resolution shows more detail. Counties often fly new imagery every few years.
Leaf-on vs leaf-off
Leaf-off imagery, flown in winter or early spring, shows ground features under deciduous trees. Leaf-on imagery shows vegetation cover.
Parcel lines on orthophotos
Parcel lines may not align perfectly with orthophotos due to parcel data accuracy and datum issues. See what is a geodetic datum. Neither should be relied on for exact boundaries.
Historic orthophotos
Older aerial photos can be orthorectified to compare with today. See how to find historic aerial photos.
Example
An assessor reviews a new 6-inch orthophoto and notices a detached garage on a parcel that is not listed on the property record card. A field check confirms it, and the record is updated.
Lidar and orthophotos
Lidar provides elevation models used to orthorectify imagery, and the two are often collected together.
Sources
Federal programs such as the National Agriculture Imagery Program provide statewide orthophotos. Counties and states often provide higher-resolution imagery.
Building lean in imagery
Standard orthophotos correct terrain distortion but not always the lean of tall buildings, which may appear tilted away from the center of the photo. True orthophotos, which correct building lean, are more expensive and used mainly in dense cities. On most rural and suburban imagery, the effect is small.
Using imagery in property research
Orthophotos can show the current position of fences, driveways, sheds, and tree lines, which helps when comparing physical features with a survey or plat. They can also show how land use changed between flights, such as new clearing or construction. For a legal boundary, a survey is still required.
Imagery dates
GIS viewers usually list the year of imagery. Check the date before relying on what the image shows.
Bottom line
An orthophoto is an aerial image corrected for distortion so it lines up with maps and can be measured. It is the base imagery in most GIS viewers. Remember that parcel lines on orthophotos are approximate. Explore aerial imagery via the Platbookmapper map.
What is an orthophoto FAQ
What is an orthophoto?
An aerial photo corrected to map accuracy.
How is an orthophoto different from a regular aerial photo?
It has distortions removed and uniform scale.
What is leaf-off imagery?
Imagery taken when deciduous trees have no leaves.
Can I measure distances on an orthophoto?
Yes, approximately, in GIS tools.
Do parcel lines match orthophotos exactly?
Not always; both have accuracy limits.