nts()) provided. The URL generated may or may not exist depending whether
or not the sheet or area is available. CanVec data is available by mapsheet
(e.g. 021H01; 1:50k), CanVec+ data is available by map area (e.g. 021H; 1:250k).
If a the ntsid provided is a 1:50k reference, a CanVec URL will be generated.
Otherwise, a CanVec+ url is generated.
canvec.url(ntsid, server = "http://ftp.geogratis.gc.ca/pub/nrcan_rncan/vector/")