# surfaceArea

##### Compute surface area of a digital elevation model.

It is often said that if Wales was flattened out it would have an area bigger than England. This function computes the surface area of a grid of heights taking into account the sloping nature of the surface.

- Keywords
- spatial

##### Usage

```
surfaceArea(m, ...)
surfaceArea.matrix(m, cellx = 1, celly = 1, byCell = FALSE)
```

##### Arguments

- m
a matrix of height values, or an object of class SpatialPixelsDataFrame or SpatialGridDataFrame.

- cellx
the size of the grid cells in the x-direction, in the same units as the height values.

- celly
the size of the grid cells in the y-direction, in the same units as the height values.

- byCell
return single value or matrix of values

- ...
ignored

##### Value

Either a single value of the total area if byCell=FALSE, or a matrix the same shape as m of individual cell surface areas if byCell=TRUE. In this case, the sum of the returned matrix should be the same value as that which is returned if byCell=FALSE.

Missing values (NA) in the input matrix are allowed. They will produce an NA in the output matrix for byCell=TRUE, and contribute zero to the total area. They also have an effect on adjacent cells - see code comments for details.

##### Methods

- obj = "matrix"
takes a matrix as input, requires cellx and celly to be set

- obj = "SpatialGridDataFrame"
takes an object of class SpatialGridDataFrame as input, and retrieves cellx and celly from this

- obj = "SpatialPixelsDataFrame"
takes an object of class SpatialPixelsDataFrame as input, and retrieves cellx and celly from this

##### References

Calculating Landscape Surface Area from Digital Elevation Models, Jeff S. Jenness Wildlife Society Bulletin, Vol. 32, No. 3 (Autumn, 2004), pp. 829-839

##### Examples

```
# NOT RUN {
surfaceArea(volcano)
image(surfaceArea(volcano,byCell=TRUE))
data(meuse.grid)
gridded(meuse.grid) = ~x+y
image(surfaceArea(meuse.grid["dist"], byCell=TRUE))
surfaceArea(meuse.grid["dist"])
# }
```

*Documentation reproduced from package sp, version 1.3-1, License: GPL (>= 2)*