Yes roughly, EC1 is the area to the south of Pentonville Rd and City road down to Holborn Viaduct and the Barbican.
The area near the north is 100% residential ( its Islington by name but my opinion is that Islington proper is North of Pentonville Road andCity Road). It gradually turns to offices the further south you go.
Even so, there's still lots of residential squares and side roads to the south if you know where to look but parking is a nightmare and a lot of the buildings are 3 or 4 story town houses with difficult windows. You have to drive round the block to do the back and only then if you can find it.