How to calculate elevation difference for two points, slope, drainage and field checks
Elevation difference is the height difference between two points and matters for drainage, roads, pipelines and earthwork.
Field takeaways
- Both points need the same elevation reference.
- Phone elevation is useful for reconnaissance, not precision delivery.
- Slope uses horizontal distance and elevation difference.
- Ellipsoidal, orthometric and project elevations should not be mixed.
- MapLab Survey helps with elevation profiles, point notes and reports.
Same datum or nothing
Elevation difference is a subtraction, but only if both heights come from the same reference. Subtracting an ellipsoidal height from an orthometric one produces a number with no meaning. Confirm both values speak the same language before you calculate.
Low gradient, high demand
On drainage at one per thousand, a five-centimetre error reverses the direction of flow. Phone GPS is not an option there; you need levelling or RTK with a check on a known point.
From difference to slope
Slope is the height difference divided by the horizontal distance, not the slope distance. Using the slope distance gives a gentler gradient than the real one, and that mistake is common on short, steep sections.
See it in action
MapLab Survey | Professional Mobile GIS, GPS Surveying & Land Measurement App
Visit the YouTube channel ->Try these steps on your own phone.
MapLab Survey handles RTK/GNSS point capture, drawing, area and volume calculations and coordinate conversion, then exports to DXF, KML/KMZ, GeoJSON, Shapefile, GeoPackage, NCZ or CSV. Capture, calculation and export work offline. Live NTRIP corrections and online basemaps need a connection.
Frequently asked questions
How is elevation difference calculated?
Subtract one elevation from the other.
Is phone elevation enough?
For reconnaissance only.
Is elevation difference the same as slope?
No.
Why does vertical reference matter?
Different references should not be mixed.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: Phone elevation · Terrain slope · Creating an elevation profile · MapLab Survey