[OSM-talk] Help to import Rio de Janeiro city data to OSM - misaligned shapefiles

[John Smith]

2010/5/14 Iván Sánchez Ortega <ivan at sanchezortega.es>:
>> Any ideas? I don't think that the government data is misaligned like
>> that.
>
> You're wrong: it is. It all comes down to which reference system you
> use. Unfortunately, you'll need two years of geodetics classes in a
> university to have a full understanding of the issue.

Maybe a full understanding, but the basic understanding is this,
originally governments used the centre of the earth as the basis,
although not always some mines in Australia used the direction of the
vein of ore as north/south even if it ran east/west.

Since the advent of satellites spinning round the globe, and more
specifically the GPS cluster of satellites, they now use the centre of
the mass of the earth.