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Draw your own calibration area

The candidate areas on the atlas were placed by rule: drawn at random across each country's building-density range, plus two start-here boxes in its densest districts with the most large roofs. They are the first choice, because nobody picked them for the solar they contain. Drawing your own is worth it when no candidate covers a kind of place the country still lacks, when a candidate turns out not to be mappable, or when you know a place well enough to outline it properly.

A drawn area does not have to be a square. An outline that follows the edge of a suburb, an industrial estate or a village is often better than a box, which clips arbitrary halves of whatever it lands on. This page shows how to draw one in JOSM, save it as GeoJSON and send it in.

Before you draw

  • Pick by landscape, never by panels. Choose the kind of place first (a dense old town, a planned suburb, a farming village) and look at the solar second. An area chosen because you can already see panels there biases the calibration before anyone maps it.
  • Keep it one kind of place. Do not mix planned housing with informal settlement, or an industrial estate with the houses next to it. A free outline makes this easy: follow the real edge.
  • For a sparse area, include the ground between the houses. An outline traced tightly around a village's built-up edge is denser than the village's surroundings, and density is what decides which part of the country an area can calibrate. If the point is to reach the sparse end, take in the fields and gardens on purpose.
  • Not around a solar farm. Ground-mounted parks are measured by the satellite model; an area sited to include one teaches the small-installation calibration the wrong thing.
  • Size. Aim for 1 to 4 km2, with the whole outline fitting inside a square of about 2.2 km: that is one satellite training window. A larger area still works but counts for less per panel mapped; a long thin shape is better sent as two or three areas.
  • No overlap with an existing area or candidate. Two overlapping areas count the shared panels twice.

1. Check the imagery date

A calibration area certifies every panel visible on the imagery you map from. If that imagery is much older than the satellite data the model reads, the area cannot be used, no matter how carefully it is mapped. Check before you draw:

  1. Open the place in iD, choose Esri World Imagery as the background and press Ctrl+Shift+B (Cmd+Shift+B on a Mac). The background panel shows the imagery's capture date for the spot you are looking at. Esri Wayback shows the same dates and the history behind them.
  2. Compare it with the Sentinel-2 dates shown under the headline figure of the country's atlas. If the oldest imagery over your area is more than about a year older than the start of that window, pick another place.

2. Draw the boundary on its own layer

  1. In JOSM, File -> New Layer (Ctrl+N). The new, empty layer becomes the active one. Drawing the boundary here, rather than on the OpenStreetMap data layer, keeps it out of what you map.
  2. Add Esri World Imagery from the Imagery menu and zoom to your area.
  3. Press A (draw) and click around the area, putting the corners on things a second mapper can see: roads, canals, walls, field edges. Close the outline by clicking the first point again, then press Esc.
  4. Leave it untagged. The outline needs no tags, and one file may hold several pieces: they are treated as one area.

Screenshot needed · save as docs/assets/figures/contribute-josm-draw-boundary.png

Show: JOSM over Esri World Imagery with a hand-drawn closed outline following roads and a canal around a neighbourhood, and the Layers panel listing the new boundary layer as the active layer, separate from any OSM data layer.

Starting from a square. The atlas's Propose a calibration area button drops a 2 km square and checks it against every existing area. Press GeoJSON in its popup, open the file in JOSM with File -> Open, and move the corners to fit the area. (Its Open in JOSM button loads the square locked, which is right for mapping but not for reshaping.)

Never upload the boundary

The outline is not an OpenStreetMap feature. JOSM still treats the new layer as a data layer, so never press Upload while it is selected. Map on the separate OSM data layer, and check the layer name in the upload dialog before you confirm.

3. Save it as GeoJSON

  1. With the boundary layer still active, File -> Save As... (Ctrl+Shift+S).
  2. In the file-type dropdown choose GeoJSON, and give the file a short name, e.g. chipata_north.geojson.

JOSM saves the whole active layer, so a layer holding only your outline gives a clean file. The Measurement panel (Windows -> Measurement) shows the area of the selected outline if you want to check the size first.

Screenshot needed · save as docs/assets/figures/contribute-josm-save-geojson.png

Show: JOSM's Save As dialog with the file-type dropdown set to GeoJSON and a file name such as chipata_north.geojson entered.

Any other tool that saves a polygon as GeoJSON in longitude/latitude works too, such as QGIS or geojson.io. iD cannot save one.

4. Check it against the existing areas

Drop the file onto the country's atlas map (or use Layers -> Add a layer). It appears as your own layer next to every calibration area and candidate, so an overlap or a near-miss is visible at once. The file stays in your browser; nothing is uploaded.

5. Send it in, then map

Send the boundary before you start mapping, and do not reshape it afterwards: a boundary redrawn around what you found is biased in the same way as one placed where panels were visible.

  1. Open a calibration area report.
  2. Area: drawn: plus the file name, e.g. drawn: chipata_north. Status: Started.
  3. Open the .geojson file in a text editor and paste its whole content into Boundary GeoJSON.
  4. Add the imagery you checked and its capture date.

A maintainer checks the outline (size, overlap, district) and answers on the report. Then map it like any other area, following the JOSM guide from step 4, with your boundary layer open beside the OSM data layer, and report it when every panel inside is mapped. If you do have to change the boundary, post the new file on the same report before mapping on.

Maintainers: a drawn boundary is registered with --geojson, see Register an area. The full rules behind this page are in the mapping protocol.