Editing (or cropping) .img files for Garmin?

I’m new at this OpenStreetmaps thing and really like that I can get free maps rather than spending $100 on maps from Garmin. Thanks!
I’ve finally figured out how to find the maps I want from http://garmin.na1400.info/routable.php (I’m in the Seattle area). I was wondering if anyone knows how I can crop the maps to cover a smaller area? I just got a Garmin eTrex Venture HC and it has 24 megs of memory. I’d like to make a long narrow map from Seattle to Portland (I’m planning on doing the STP bike ride this summer) but not sure how I can just get this path into the GPS.
What is the easy way to do this? I’m sure there is an application out there, there seems to be a LOT for this.



If you have the time and inclination, you can roll your own maps using mkgmap. This way you can just create a map for the very specific area you’re interested in which will create a smaller file. See my website for tips if you want to do this.

If not, you may be able to crop the map using GPSMapEdit. Freegeographytools has run a very good series of posts on apps for use with Garmin.
and more generally
http://freegeographytools.com/2010/03 and http://freegeographytools.com/2010/04

Thanks, I’ll check out your sites. I’ve mostly been trying to get this all working in Ubuntu Linux 10.04 and mostly have it going, but just can’t send the maps to the GPS yet. Still working on that, so I have to boot over to Window 7 and upload it.
Ive been using the “MapUpload” software to get the .img file into my gps, but when I check the “Add to existing maps” I still seem to lose something. Not sure what I’m doing wrong. I did download the full Seattle Area into the gps the other day from the site I mentioned above, but would like to make a long skinny map from Seattle to Portland that fits in 24 megs and has memory leftover to plot my trip.

anyway, I’ll check out the sites you posted. Thanks for the advice!