Creating polylines/boundaries from messy OS map

Hi all, hope it's okay for me to sign up here and post a question. It's my first post but I'd like to stick around and glean as much knowledge from this place as possible as well as give back what I can!

I'm having real difficulty with a large survey plan that I need to tidy up for a laser cut model.

I'm using autocad 2010, but also have access to other software (vectorworks, archicad etc) if they have specific tools which will help. (I'm an architecture student).

Unlike UK os maps which have building outlines and intermediate walls on seperate layers, the plan I have (for turkey) has every every building as a closed polyline. Therefore, where buildings are adjacent to each other, the lines all cross over, and don't line up great either.

I would like to draw a polyline round the perimeter of each city block and delete the internal walls/mess.

I've tried gridding off the plan and using the boundary tool to select the 'negative' space around buildings (it's currently just a figureground drawing) in the hope that it will trace round each block, but that didn't work.

So... Currently I am exploding everything, deleting internal walls, tidying things up, then polylining it all back together again.

Hope this pic illustrates what I'm trying to say, orange has been done, blue is left to do, the selected polyline is part of a typical city block that needs to be turned in to one polyline round the extents of the block.

Have you tried drawing a rectangle to totally enclose one block (it doesn't matter if the edges of other blocks come into the rectangle), and then use Bpoly?

Incidentally, I don't suppose that the Ordnance Survey would care too much for your describing their maps as messy.

Hi eldon, thanks for the reply.

I did try that earlier with the boundary tool (same thing right?) with not much success. Tried again but drawing a smaller rectangle (i.e. one block at a time) and it worked a lot better so thanks for that.

Sorry my title is misleading, I wasn't being rude about ordinance survey! They're great as all the internal walls are on a separate layer so this task would be a doddle, however this drawing is of Istanbul and they're not quite so helpful!

I think that one city block at a time would probably be less taxing for AutoCAD.

It does need a bit of erasing of surplus bits, but that is quicker than exploding and trimming and then rejoining.

Boundary tool is the same as Bpoly.

Ordnance Survey (note spelling) is the British mapping agency, so would be surprised to be credited with Turkish mapping