Measuring a plot on the map
Napi (Survey Office) cadastral sheets are not on public web maps, so this tool measures the shape you draw on top of the base map. It works best where the plot boundary is visible: compound walls, roads, field bunds and ridges. Switch to the Satellite layer, zoom in until the plot fills the screen, then click each corner in order around the boundary. Click the first corner again, or Finish, to close the shape.
Every corner can be dragged afterwards. Undo removes the last corner, Clear starts again, and Locate me jumps to where you are standing, which is the quickest way to find a plot you are on. Each side shows its length on the map while you draw.
How the area is worked out
Each corner is a latitude and longitude. The area is computed on the WGS84 sphere (radius 6,378,137 m) with the standard ring formula used by GIS software, so it is right for any plot anywhere in Nepal, with no map projection involved. Sides are great-circle distances. The result is then converted exactly through square feet: 1 ropani = 5,476 sq ft and 1 bigha = 72,900 sq ft, the same numbers as the Ropani–Aana converter.
Worked example: a square plot 74 ft (22.56 m) on each side is 5,476 sq ft = 508.74 m² = exactly 1 ropani, shown as 1 ropani 0 aana 0 paisa 0 daam, or 0 bigha 1 kattha 10.05 dhur in the Terai system.
How accurate it is
Satellite imagery can sit a few metres off the ground it shows, and a click can land a metre or two from the true corner. On a 20 m × 25 m plot, one metre of error on every side changes the area by about 8%, so treat the result as a check, not a survey. A larger plot measured carefully at high zoom comes out within a few percent of the Napi figure.
Tall buildings lean in imagery, so click the base of walls, not the roof edge. Include only land you own: the road setback and the public drain outside the wall are not part of the plot.
Where it matters
Checking a plot you are about to buy against the area written on the Lalpurja, estimating how much land is left after a road widening, splitting a field between heirs before the formal survey, or getting a quick area for a boundary wall or fencing estimate.