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I have a topographic map with Buildings, Roads, Hydro and land use as the prominent layers in polygon format. Also i have newly collected Building polygons of the same area in shape file format. Now i need to have an overlay analysis of Buildings in these two resources. I can rasterize and geocode the map to orient with Digital data. Also these two can be overlaid and compared manually. But i need to do this analysis automatically with possibly using a shorter method. One possibility is to vectorize Buildings in the map and perform vector overlay. However I am looking at a more efficient method possibly filtering Buildings in raster and comparing it with Buildings converted to rater in shape file. Any idea on this is appreciated.

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If you have clean topographic map (that means that bulidings have the same colour, not different shades) it is the easiest thing to do reclassification (1-buildings, 0-everything else). Then you can rasterize your polygon file showing new buildings (be careful and use the same resolution, width and height as your topo map so they will match). Then you can make a comparison.. You can also vectorize your topo map. There are different methods to do that. For example Feature analyst for arcgis can do this but it is a bit harder if your map is not clean (if you have a scan or a photo of a map). Or you can also use coreldraw (Trace module), make vektor file and then import it into gis...

cheers! Rok

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Could you bit explain about reclassification? Which software i can use and how briefly. – Sanjeewa Oct 29 '12 at 10:14
There are a lot of programmes that can do that. Arcgis, Idrisi (commercial) or SAGA (free) ... Which one do you know/use? The general workflow is the same: for each existing value you have to define new value. What kind of raster type do you have (jpg, tif, ...)? – Rok Oct 30 '12 at 10:22
Thanks. I know ArcGIS. The raster type i have is tiff. Any idea for raster classification if building has different colours. How about vectorizing with coreldraw trace module? Is it semi-automatic? – Sanjeewa Oct 30 '12 at 11:23
If you have buildings in different shades and colours it is a bit harder. It depends how big your area of interest is. You can try trace module but probably you will have to check and correct all the errors. You should just try. Sometimes it is also easier just to digitize manualy.. – Rok Oct 31 '12 at 20:27

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