Draw & Measure¶

Two tools in the Tool Ribbon let you create geometry and take spatial measurements directly on the map canvas — no external GIS required.

Measure Tool 📏¶

Click the 📏 icon to activate the Measure tool. Two modes are available:

Mode	How to use
Distance	Click two or more points on the map; each segment label shows its length; a running total appears at the endpoint
Area	Click three or more points to define a polygon; the enclosed area is displayed in km² or ha

Press ESC or double-click the last point to finish a measurement
Click 📏 again (or switch tools) to cancel and clear the overlay
Measurements are temporary — they are not saved to the workspace or exported

Accuracy notes

Distance uses the Haversine formula (great-circle, sub-metre accuracy at basin scale)
Area uses a 2-D planar approximation from projected Web Mercator coordinates — accurate to ~1 % for basins up to 100,000 km²; for precise area calculations on large regions use the Python analysis tools

Click the ✏️ icon to sketch geometry that can be saved as a vector file and used as a region of interest (ROI) for analysis tools.

Mode	How to draw
⬡ Polygon	Click each vertex; double-click to close
〰 Line	Click each vertex; double-click to finish
● Point	Single click to place

A green draft overlay appears on the map, and three action buttons appear at the bottom of the panel:

Button	Action
Save	Writes `vectors/<name>.geojson` in the workspace root, registers the geometry as the active ROI under `sessionId='map'`, and adds it as a layer
Export	Downloads the draft as a `.geojson` file to your Downloads folder without saving to the workspace
Discard	Clears the draft without saving

Once saved, the geometry is immediately available to all MCP analysis tools through the active session:

# Any tool that accepts sessionId will use the drawn ROI
delineate_watershed(session_id="map")
compute_twi(session_id="map")

The layer also appears in the Layers panel under its file name and can be styled, exported, or removed like any other vector layer.

Draw a rough watershed outline before running delineate_watershed to constrain the search area
Use a polygon to clip a raster before requesting a transect — the polygon saves as the session ROI automatically
Saved vectors are plain GeoJSON — open them in QGIS or load them into geopandas at any time