Map drawer

A quick measurement

To measure a walking loop, choose Line and click along the path. The length updates after each click in kilometers and miles. To measure a field or a lake, choose Polygon and click around its edge. After the third point the shape closes itself, and the tool adds the closing edge to the perimeter and reports the enclosed area in square miles and acres.

How to use it

1. Choose Line for a path or Polygon for an area.
2. Click the map to add points in order. A marker appears at each click.
3. For a line, read the running length under the buttons. For a polygon, after three points the shape fills and the line gives its perimeter and area.
4. You can switch between Line and Polygon at any time; the same points are redrawn. Clear removes everything.

How lengths and areas are measured

Each segment is a great-circle distance from the haversine formula on a sphere of radius 6,371.0088 km, and the length is the sum of the segments. For a polygon the area comes from the spherical polygon formula, which sums a term for each edge from its change in longitude and the sines of its latitudes.

Because both work on the sphere, the results stay correct for large shapes where a flat calculation on the Mercator map would be far off.

Tips for precise results

Zoom in before clicking: each click lands where the map puts your pointer, so a zoomed-out click can miss a road by hundreds of meters. Add more points on curves, since the tool joins points with straight segments.

Keep polygon edges from crossing. A shape that crosses itself has no meaningful area.

When another tool fits better

For area only, with acres and hectares shown side by side and an undo button, use the map area calculator. For a route between towns, the multi-stop distance tool adds search and a driving total. To follow the terrain along a line, the elevation profile samples heights.

Common uses

Runners and walkers use a line to measure a route before heading out. Gardeners and farmers use a polygon to get the area of a plot in acres. Planners sketch a boundary to see how big it is. The drawing is not saved, so write down the numbers or take a screenshot before leaving the page.