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Field manual · 09/17

Terrain Analysis

Terrain analysis answers the questions a contour map makes you work out for yourself: what can be seen from here, whether those two points can see each other, how steep that slope is, and how high the ground is. Most of it runs on-device and works offline once the elevation data is downloaded.

where the elevation comes from

Everything in this chapter runs on a digital elevation model. Resolution depends on where you are: 1 arc-second (about 30 m) across North America, Europe, Japan and New Zealand, and 3 arc-second (about 90 m) elsewhere.

Data is fetched as needed and cached. Include Terrain Data when creating an offline region downloads it deliberately, so contours and analysis keep working with no signal.
A GeoPackage containing gridded elevation coverage feeds the same stack — useful where you have better national data than the global model. See Import, Export & Backup.
Modelled elevation is reference data, not survey data. It describes the ground surface, not buildings or vegetation, and a 30 m grid cannot see a gully narrower than 30 m. Treat a viewshed as a good first answer, not a guarantee.

viewshed

Shades everything visible from the map centre against everything hidden from it — the fastest way to find dead ground, site an observation post, or work out where you can be seen from.

  1. Put the map centre on the observer's position.
  2. Open Tools → Viewshed and set the Radius — a slider from 0.5 km upwards, in 0.5 km steps.
  3. Read the shading: visible terrain against terrain in defilade.
The radius is capped at 5 km on the free tier and 20 km with Pro. A larger radius takes longer to compute and needs more elevation data.
Viewshed is symmetrical: ground that can see you is ground you can see. It works equally well for choosing a route that stays out of view.

line of sight

Two points, one question: can they see each other? Place an observer and a target and the tool returns a verdict plus the numbers behind it.

Distance
Ground distance between the two points
Slant Range
True line-of-sight distance, including height difference
Bearing
Observer to target, in your north reference
Vertical Angle
Angle of elevation or depression to the target
Observer Elev.
Ground height under the observer
Target Elev.
Ground height under the target
Elevation Δ
Height difference
Highest Terrain
The highest ground along the path
The verdict reads Clear Line of Sight — target is visible from the observer — or Obstructed, with the distance at which the path is blocked. That distance tells you how far forward to move.
The elevation chart draws the terrain profile with the visible stretch in green, the blocked stretch in red and the ground in brown. The verdict and every metric above are free; the chart itself is part of Pro.
This is the tool for radio planning as well as observation — a VHF link and an eyeball are blocked by the same ridge.
Line of sight between two points with the terrain profile and a blocked verdict
Line of sight

slope PRO

Slope Angle

Shades the visible terrain by steepness, highlighting 27° and above — the threshold that matters for avalanche awareness and for vehicle go/no-go. It covers the visible map area up to about 40 km across and tells you the current coverage as you zoom.

Slope Between Points

Draw a path and get the inclination leg by leg: Total Length, Total Ascent, Total Descent, Average Incline, the Steepest Leg with its number, and a slope profile. Save Path to Layer keeps the result.

Slope Angle answers "is this face too steep"; Slope Between Points answers "how hard is this specific climb". Use the first to choose a route and the second to plan it.

contour lines PRO

Draws elevation contours over any base map, satellite imagery included — so you can have imagery and terrain shape at once instead of choosing between them.

Pick the Interval to suit the ground: tight intervals for gentle terrain, wider ones in mountains where close contours would merge into a solid block.
Contours are computed on the device. Once the elevation data for an area is downloaded, they work with no internet connection at all.
Coverage is the visible map area up to about 40 km across. The panel states the current coverage in kilometres so you know when to zoom in.
OpenTopoMap and the Carto topo map already have contours printed into their tiles. This tool is for putting contours on maps that lack them — satellite, road maps, imported imagery.

elevation and sea depth PRO

Elevation

Ground height at the map centre, with Incline and Aspect — how steep the ground is there and which way it faces. Aspect matters for sun, wind, snow and cover.

Sea Depth

Water depth under the map centre, from bathymetric data.

The two tools cross-refer. Reading 0 m of terrain over water suggests the Sea Depth tool; asking for depth on dry land points you back at Elevation.
Both need an internet connection unless the area's data has been downloaded.
Save a reading as an elevation point or depth point and it becomes a permanent item carrying the date it was read. See Pins & Shapes.
An elevation profile along a route with grade colouring
Elevation profile

elevation offline

Terrain analysis without a signal needs the elevation data on the device first.

  1. Open Map Type → Offline Maps → Add Offline Region.
  2. Box the area and leave Include Terrain Data switched on.
  3. Download. Contours, viewshed, line of sight, slope and spot elevation then work offline across that box.
Terrain data is separate from map tiles — an area can have maps but no elevation, which is why the tools can fail on a region you have already downloaded imagery for.
When data is missing the tools say so plainly: No elevation data is available for this location., or Could not load elevation data. Check your internet connection. with a Try Again button.

ar view PRO

Holds the camera up to the landscape and labels it. Peaks within 50 km are named with their altitude, your own pins are drawn where they really are, and the sun and moon arcs show where the light will be.

Your pins in the landscape

Pins from the active and visible layers within 10 km are projected onto the camera view with their map symbol and live distance, and are never hidden behind terrain — a waypoint behind a ridge still shows you which way it is.

The skyline corrects the compass

The app computes the terrain silhouette for your position and matches it against the real skyline in the camera. Locking the two together corrects compass error, which is what makes the labels sit on the right summits instead of drifting.

It works offline once the elevation data is cached — the peak list and the silhouette are both computed on the device.
AR Navigation to a specific pin is the same engine with a target reticle. See Navigation & Directions.
Free users get one full-length AR session. It is shown as "1 free preview left" rather than a padlock, because what AR is worth depends entirely on the horizon you happen to be standing in front of.