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Shapefiles Don't Align Properly   D. O. Morris Jan 26, 2009
Re: Shapefiles Don't Align Properly   Chris Beckcom Jan 27, 2009
Re: Shapefiles Don't Align Properly   Will Pridham Jan 29, 2009
Re: Shapefiles Don't Align Properly   D. O. Morris Jan 29, 2009
Re: Shapefiles Don't Align Properly   Will Pridham Jan 29, 2009
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Subject Shapefiles Don't Align Properly 
Author D. O. Morris 
Date Jan 26, 2009 
Message I am working with two 3 different shapefiles of which I know one definite GCS: NAD 83. I have brought that shapefile into an empty map to set up my data frame reference system. Then I had a pipeline shapefile with no projection that should be in Maryland State Plane. I also have a pipeline shapefile originated from CAD data with no projection. I haven't any source data for this last CAD conversion and therefore don't know which datum / coordinate system it was created in. I have tried defining the project as I did for the other file with no luck. I have also tried other coordinate systems to try and guess. I can see the file but it is definitely not aligned properly.

Any tips on how to make this align? If I was able to align one without the projection I should be able to align the other if I find the correct type it was made in...right?

Thanks!
   
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Subject Re: Shapefiles Don't Align Properly 
Author Chris Beckcom 
Date Jan 27, 2009 
Message CAD data is notorious for not being in any projection nor datum. Frequently it is in an assumed coordinate system in surface units with an arbitrary origin at something like 5000,5000. If that is the case here you'll have to warp(transform) it to make it fit. Another possibility is the units the CAD drawing are something different than what you're using, ie the drawing was in feet and you're in meters. So you would need to scale the drawing geometry down to match. The list can go on and on when dealing with CAD files.

Chris 
   
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Subject Re: Shapefiles Don't Align Properly 
Author Will Pridham 
Date Jan 29, 2009 
Message I work with CAD and GIS on a daily basis and I echo the last poster's sentiments. Arbitrary coordinates don't translate well into GIS.

The only way I know is by trail and error. I "drag and drop" shift, tweak and whatever it takes to get the most accurate positioning. Most of the time though it won't be precise.

Its not an ESRI issue, its a survey methodology issue.

I actually state on every map that includes AutoCAD overlays (developments in this case), that the map isn't a precise indicator of where the development lies in the real world, however it is relatively accurate with respect to mapped features. 
   
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Subject Re: Shapefiles Don't Align Properly 
Author D. O. Morris 
Date Jan 29, 2009 
Message Thank you for your replie (s). When you say drag and drop and tweak, I have tried various coordinate systems and datums. I thought NAD 83 HARN would be the most likely? I am working in VA South State Plane...I have tried others as well. Any other tips I feel like there has to be something I'm missing - it's nowhere near close. 
   
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Subject Re: Shapefiles Don't Align Properly 
Author Will Pridham 
Date Jan 29, 2009 
Message They rarely are unless they've been created "properly". Let me guess, the CAD drawing is way off the screen!?

I usually make sure that I don't need to change the scale factor in AutoCAD for the DWG before its imported into ArcGIS. Try changing it to "1" and seeing if it at least is the correct proportions. If not, then you'll have to use the georeferencing tools to reference the CAD drawing to GIS features such as road intersections.