[R-sig-Geo] Scaling the scale bar

[Alexander Sommer]

Wow, that was a quick response. Thank you, Edzer!

My apologies for adding /+/ and />/ to the code, I was not sure how to mark R code as such and separate it from the rest of the text. And I always get puzzled which operating system accepts which separator. Thought Windows rejects slashes, but that turned out wrong. Sorry.

The code works just fine for that example, but my question was rather how do I know the scale? And how can I make sure it is the correct one? (In the example: How do I know it is 100000 and not something else? Is the bar really representing 100 km?) For example, when I run

 States <- spTransform(States, CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"))

after /readOGR/
 
 scale  = 100000

seems to be wrong. How can I find out the correct scale? In a perfect world I would like to have some formula like /Length, I like to represent × Something from projection, bbox or whatever/. 

Once again, thanks for your help

Alex


-- 
Alexander Sommer
Forschungsverbund Deutsches Jugendinstitut/Technische Universität Dortmund