Slope Maps for Building on Sloping Land in Oregon
How steep is the site, how much of it is actually buildable, and which way does it face? Measured across any Oregon property from the USGS 3DEP lidar elevation model.
Measure a site now
Search an address, click the property, and get slope in degrees shaded across the whole site.
Open the slope tool →“It's a bit sloping” is not a number
Sloping land is priced, designed and permitted differently from flat land, and the difference between a gentle lot and a steep one can be the difference between a slab on grade and a stepped foundation with an engineer's report. Yet what most people have when they make an offer, or brief a designer, is a photograph and an impression.
The elevation data to answer this properly is public. DOGAMI reports about 99% of Oregon covered by at least one lidar project. The USGS publishes the result as a bare-earth model, 3.3 ft per pixel where lidar exists. What has been missing is a way to point it at one property without installing GIS software.
What slope means for a site
Slope is how quickly the ground rises or falls, shown here in degrees. It helps to have a feel for what the bands mean in practice, because the same number has very different consequences depending on what you are doing.
| Slope | Roughly | What it means on the ground |
|---|---|---|
| 0–10° | 0–18% | The gentlest band in the property report. Where building pads, driveways and workable fields are easiest to find. |
| 10–20° | 18–36% | Noticeably sloping. Building and access ask more of the design and the earthwork as you move up the band. |
| 20–25° | 36–47% | Steep. A question for your designer and the county, worth raising early. |
| 25°+ | 47%+ | The steepest band the report shows. Ask your county planning department what applies before you plan on it. |
These are orientation, not rules. No legal thresholds are stated here: what governs a building permit on a sloping lot is your county or city's requirements, the building method and any hazard mapping that applies to the site. Check with your county planning department.
Why the distribution beats the average
A single average slope is close to useless for a real property. A parcel that is half flat bench and half steep face averages out to a moderate number that describes no part of the site.
What you want is the distribution: how much ground sits in each band. That turns straight into decisions. “Most of this parcel is under 10°” tells a farmer how much is workable; “there is a flat area in the northwest corner” tells a designer where the house goes. The Slope & Aspect tool shades slope across the site so you can see where each band lies, and the Property Report gives the share of the taxlot under 10°, 10–20°, 20–25° and over 25°.
Aspect: the half of the answer people forget
Aspect is the compass direction a slope faces, and in Oregon it matters more than most people expect. Two lots with the same steepness, a few hundred feet apart, can be very different places to live because one faces south and the other north.
- Sun. In the northern hemisphere south-facing slopes collect the most sun. North-facing slopes stay shaded longer, and around the winter solstice on December 21 a steep north face can see little direct sun at all. The Sunlight tool models it hour by hour.
- Damp, frost and snow. North faces dry slowly, hold frost and snow longer and grow moss on driveways and decks — in a Willamette Valley winter and in Bend's high desert alike.
- Growth. Pasture, gardens and orchards grow differently on different faces; aspect is a large part of why one field does better than another.
- Wind. Aspect combined with the prevailing wind decides exposure — a slope open to the wind in the Columbia Gorge is not the same proposition as a sheltered one.
The slope tool returns a full aspect distribution alongside slope, so you can see how much of a property faces each direction rather than guessing from the contours.
The rest of the site assessment
Slope is one layer. These run on the same property boundary, from the same lidar.
How to run a slope assessment on a site
- Select the property. Search the address and click the parcel so the analysis uses the county taxlot rather than a rectangle that includes the neighbor's bank.
- Check the lidar first. Confirm your area has lidar coverage and note the flight year on the coverage page. Slope from the coarser fallback is not reliable on gentle ground, and an older flight will not show recent grading.
- Run slope, then aspect. Find the gentle ground, then see which way it faces. Where “gentle” and “south-facing” overlap is usually where you want to be.
- Cross-check drainage. Flat ground at the bottom of a catchment is flat because water put it there. Run the Water & Drainage tool over the same boundary before you settle on a site.
- Export for whoever needs it. Contours as DXF for the designer, the terrain report as a PDF for the file, or the elevation model as a GeoTIFF if an engineer wants the surface itself.
Where this stops and a professional starts
Slope analysis from lidar is a measurement of the ground surface. It is excellent for narrowing options, checking a listing's description, briefing a designer and preparing for a conversation with the county. It is not a geotechnical assessment, and it cannot see what is under the surface — soil, groundwater, fill, old landslide material and rock all matter enormously on sloping land, and none of them appear in a DEM. DOGAMI's hazard maps show mapped landslide hazard.
Where a building permit, a foundation design or a stability question is involved, this is the input to the conversation, not the conclusion. Ask your county planning department what it needs, and engage a geotechnical engineer and a licensed land surveyor where it applies.
Related guides
- Contour map of your property — contours over the taxlot, exportable for CAD.
- Terrain checks before buying rural land — the full pre-offer pass.
- Lidar coverage in Oregon — resolution and flight year for your area.
- Elevation lookup — the ground elevation at a single point.
Frequently asked questions
How do I find out how steep my lot is?
Select the property on the map and run the Slope & Aspect tool. It reads the USGS 3DEP elevation model across the site, shades slope in degrees and reports the minimum, mean and maximum. For the share of the land in each steepness band, run the Property Report on the same taxlot. The bands are more useful than a single average, because most lots are a mix of flat and steep ground.
What slope counts as a steep lot in Oregon?
There is no single statewide number this site can give you; what applies depends on your county or city and on how you build. The property report uses four bands — under 10° (about 18%), 10–20°, 20–25° and over 25° (about 47%) — to show how much of a lot falls in each. These are not legal thresholds — check with your county planning department.
Will the county accept a lidar slope analysis with a building permit?
Only your county planning department can say for your application. Lidar slope analysis is widely used for site analysis and early planning, and it is a good way to show which part of a lot you intend to build on. Where the county needs surveyed elevations, a geotechnical report or engineered design, it will tell you, and those come from licensed professionals.
Why does aspect matter as much as slope?
Aspect is the compass direction a slope faces, and in Oregon it decides how much sun a site gets. A south-facing slope collects sun through the day and dries out; a north-facing slope of the same steepness stays cooler, damper and shadier through winter, which affects where the living room goes, how snow and frost linger, and whether a driveway ices over.
Can slope analysis show me where to put the house?
It shows where the buildable ground is, which is most of the work. Find the areas under the slope you are comfortable with, then check them for what slope cannot see: setbacks and zoning, flow paths, existing services, sun through the day, the access grade from the road, and views. The slope map narrows a lot down to two or three candidate sites; site knowledge and a designer choose between them.
How accurate is slope from a lidar DEM?
Slope is a derivative of elevation, so it amplifies whatever error the elevation carries. On steep ground with good lidar the result is reliable. On very gentle ground the model’s own noise becomes a meaningful share of the signal, so treat near-flat readings as approximate. Where no lidar work unit exists and the model falls back to coarser 1/3 arc-second data, slope on gentle land is not trustworthy; check coverage first.
What does the slope distribution give me?
The Property Report breaks a taxlot into slope bands — under 10°, 10–20°, 20–25° and over 25° — as a share of its area. That converts directly into practical questions: how much of the land is workable, how much of a lot is buildable without retaining walls, or how much of a field is steeper than you want to drive a tractor on.