I want to reproject OpenStreetMap roads data from the current projection (WGS 84) to UTM, since I read in another GIS.SE discussion (How to get $length in meters in QGIS?) that WGS 84 cannot be used to measure length in m or km. My end goal is to calculate the total roadway kilometres within each district, so that I can enter that variable into my regression model. The country in question is Indonesia, and as you can see from the map below, it covers UTM zones 46-54.
Image source: Wikimedia, http://upload.wikimedia.org/wikipedia/commons/e/ed/Utm-zones.jpg
Does it really matter which one I choose? Can I choose the one that’s roughly in the middle and call it good (that would be zone 50) or should I pick the zone that is more densely populated with roads (Jakarta/Java, zone 48)?
I am only barely functionally literate in GIS. The only formal training I had was a 3-day course back in 2008. Really, the only reason I need the roadway kms variable was because one of my thesis committee members wanted me to account for it in my model…
And to confirm, once I have reprojected to the UTM CRS, I can use my GIS software’s built-in length tool to directly calculate the length in metres (or divide by 1000 for km), right?
I am using QGIS.