[R] User defined grid on map

Ray Brownrigg
Wed, 11 Apr 2007 22:33:53 -0000

On Thu, 12 Apr 2007, Adriana Bejarano wrote:
> This may be a trivial question for some of you: Is there a way to add
> defined grid sizes on specific areas of a map?. I want to add 10kmx10km
> grids to all California coastal counties:
>
> "california,alameda", "california,contra costa",
"california,del norte",
> "california,humboldt", "california,los angeles",
"california,marin",
> "california,mendocino" ,"california,monterey",
"california,napa",
> "california,orange", "california,riverside",
"california,sacramento",
> "california,san benito", "california,san bernardino",
"california,san
> diego" , "california,san francisco", "california,san
joaquin",
> "california,san luis obispo", "california,san mateo",
"california,santa
> barbara", "california,santa clara", "california,santa
cruz",
> "california,siskiyou", "california,solano",
"california,sonoma",
> "california,sutter", "california,trinity",
"california,ventura",
> "california,yolo"
>
The mapproj package has a map.grid() function, but that only allows you to
specify latitude- and longitude-based grids.  I don't think it would be too
difficult to roll your own using standard trigonometry if you weren't too
worried about the non-sphericity of the earth.

Otherwise I guess there would be something 'out there' to provide you
with
some conversion between lat/long and distance from a fixed point.

HTH,
Ray Brownrigg