Where can I find shapefiles for 1kmx1km grid (UTM grid) for the entire USA? It seems everywhere that I looked at there were shapefiles for states separately or for some particular UTM zones. I don't want to end up join 50 shapefiles.
I really don't know a better way to explain this but I will try. You cannot find the data-set because the projections are different for each zone since the "Zone" is in reference to a Projected Coordinate system which the data is in.
For example, Iowa has two zones so there are two separate files, one for UTM zone 14 and one for UTM zone 15. If you combined the different shp files your projection would be off for one if not both of the zones. You could always read up about Projected Coordinate Systems to get a better understanding the the concept. If you managed to merge all the zones together it would be a useless dataset (since the grids would be all sorts of skewed) thus defeating the purpose the the National Grid system in the first place. If you try to merge the shp files in ArcMap you will probably get an error caused by the different projections too. Hope I didn't come off harsh.