Elevation, relief, and slope answer different questions
- Center elevation is the 3DEP elevation returned at the selected coordinate.
- Local relief is the difference between the highest and lowest of the nine nearby samples.
- Local slope estimates the grade and downhill direction across that small sample grid.
The estimate is local, not parcel-wide
The default grid extends around the selected point. It can miss changes elsewhere on a lot, especially when the address geocoder places the point along a road segment rather than on a building or parcel centroid. Retaining walls, curbs, drains, culverts, vegetation, and subsurface water flow are outside the model.
Use the slope result to form better questions for a site visit. Do not use it as a grading plan, drainage design, legal elevation, or construction approval.
Why a field survey can differ
Digital elevation models represent a gridded bare-earth surface at the available source resolution. Collection date, source quality, terrain change, interpolation, and the exact location sampled all affect the comparison with a current survey.