これは地図に経緯度が使われるようになってからの習慣であって、古い地図には南が上のものも多い。 (source: line 8-9)
What does this これ represent? I guess it shall somehow pick up what was said before, but for that, I learnt that そ- is used. So I'd like to know whether it does the same thing as そ- here or something else.
から I guess this から has a temporal function and confers anteriority here? Since I have issues with the sentence in general, I'd like to confirm this, because I really don't know whether my interpretation of the sentence is reliable or not with so many uncertainties around...^^
て-form of である right?
I really don't know what to make of this. First, もの. What is it? I guess its 物, but I'm not 100% sure. Second, as I said, I have no idea what to do with this phrase. I don't really know what to do with the particle も here, and while I do know that Japanese can work perfectly with nominal phrases only, I simply don't know what this part wants to tell me content-wise.
To give an overview how I interpreted these elements in context, here's my try at translating it as far as I could:
This since on maps longitude and latitude being used habit being there, on old maps the south has many upper things/things on top.
In my interpretation, I treated the parts in italics as one syntactical unit. Their correlate in the Japanese original would be これは...習慣であって.