Request about area and perimeter

[Tania Escalante]

Hi everyone,

Can you help me please? I've not clear how CosnNet calculates area and perimeter of a solution. I'm trying to calculate those parameters on SIG and the results are different to ConsNet.

Do you know some reference to this?

Thank you so much...

Tania Escalante

[Michael Ciarleglio]

Hi Tania,

The area is always calculated as the sum of all of the area of the cells which are included in the conservation network.  The 'perimeter' will only include the exposed perimeter between cells that are included in the network, and cells that are not included.

We obtain these values from the area and perimeter of individual cells.  Three cases:

(1) If you are using a square grid, evenly spaced at a regular distance, then each cell represents a perfect square.  The area and perimeter are calculated using the grid spacing.

(2) If you are using a grid, with evenly spaced lat-long coordinates, then each cell represents a piece of a sphere.  At the equator the shape would be close to a square, but at higher latitudes, the shape becomes more like a curved trapezoid.  In this case, the perimeter is calculated using a Haversine formula with earth radius of 6372.79548 (meters).  The calculation of the area looks to be derived from the surface area of a sphere, but I need to double check that formula.

(3) If you provided your own cell geometries, it is based on the area and perimeter in the Consnet cell shape input file.

 

How far off are the values you observed?  Perhaps I need to check something in the ConsNet code!

mc