For every block of land, its perimeter is equal to 4 - # of land neighbors. Sum up all these values to get the total perimeter.

```
def islandPerimeter(self, grid):
width = len(grid[0])
height = len(grid)
perimeter = 0
for y in range(height):
for x in range(width):
if grid[y][x] == 0:
continue
numOneNeighbors = int(y > 0 and grid[y-1][x] == 1) + int(x > 0 and grid[y][x-1] == 1) + int(y+ 1 < height and grid[y+1][x] == 1) + int(x + 1 < width and grid[y][x+1] == 1)
perimeter += (4 - numOneNeighbors)
return perimeter
```