qgis - CAD line drawing to GIS polygons

I'm a (reasonably) proficient GIS user (mostly QGIS, but some Arc GIS) who has been thrown the conundrum of converting/importing CAD urban planning drawings (2D drawings produce in AutoCAD 2014) to GIS shapefiles (or similar).

I have had some success in importing the drawings, but have realised that all of the drawings have been produced as lines (not polylines or polygons) which means I am losing a layer of detail that would be really very useful in GIS.

For example, I have a site plan of a new housing layout which shows hundreds of individual plots of land, which 'look' like polygons but are actually represented in AutoCAD as lines. As I understand it from reading through forum posts here it's probably best that these plots are converted to polygons in AutoCAD before we attempt to export/import them to GIS?

I'm really just looking for a solid enough workflow to produce 2D architectural plans in AutoCAD and import them to GIS so that I can now attach additional attributes to individual polygons (e.g. buildings, plots) and polylines (roads, rivers etc).

As anyone come across any useful resources that would point me in the right direction?!

Answer

For the most part, CAD doesn't deal in polygons the same way that GIS software does. You have a couple options.

1. Develop a workflow that converts your CAD drawings into a GIS format and then merges the lines into polygons based on a common attribute or vertices. The Feature to Polygon tool in ArcGIS is commonly used in this process. For example, if the lines representing your plot can be assigned a shared attribute (e.g. PlotID = 4) this is a simple task and can be handled on the GIS end.


2. Use software that is designed for this type of conversion, the primary example being FME. This may or may not be a simple solution depending the current state of your data.


3. If you want to get fancy you can intergrate the data using a topology. This would be something like using a Parcel Fabric, but would be a more complex version of option 1.

From your question I'd lean towards refining a GIS workflow using an existing set of tools. Start with one set of data (e.g. a plot of land) and develop the methodology step-by-step. I'd recommend creating a new question with an example set of data.