French to English Tech/Engineering Construction / Civil Engineering Bidding process

When quoting for a new construction job (relating to telecoms networks) the potential contractor must provide in his quote prices for two 'levels of service'.

"* Niveau bas - mise à jour du plan du bâtiment exclusivement.
* Niveau haut - mise à jour du plan d’ensemble de la station (bâtiment, emprise des différents ouvrages piste, etc.)."

I can't for the life of me work out the 'emprise des différents ouvrages piste' part of the sentence, as 'emprise' I've mostly encountered in the sense of 'expropriation' or suchlike, which doesn't seem to fit here, unless I'm reading the whole thing incorrectly.

Any enlightenment would be much appreciated.

TIA

Vicky