COGO and Legal Descriptions

01-06-2014 08:03 AM
New Contributor
I successfully used the COGO traverse tool to create a polygon for a piece of property described in a legal description. My issue arose because it did not line up with data I already have of the area. I did not expect it to line up perfectly, but I did expect it to be closer than it was. The projections for all of the data in the map are the same so I'm not sure if it is because there is a specific projection used for legal descriptions or what. If anyone has experience with COGO and legal descriptions I would appreciate the help.

I am using ArcMap 10.2.

The data I already have for the area is vast, but I am using a buildings feature class (polygon features), and a quarter section feature class (polygon features) from the datasets in our database. I also have a georeferenced image in my map that shows the property boundary surrounding the particular apartments I am looking at. This image is based on the legal description and comes from the engineers who worked on the apartment complex. Again, all data is set to the same projection.

My steps include: 1. Creating a polyline shapfile and a polygon shapefile.
2. In my editor toolbar I went to editing options and changed the "Direction Type" to Quadrant Bearing, and the "Direction Units" to Degrees Minutes Seconds. I checked the "Ground to Grid Connection" box, then I made the "Distance Factor" 1 since my projection is in State Plane US Feet. 3. I started an editing session and began using the COGO traverse tool to create a polyline feature that according to the legal description commences at the corner of section 28 (remember I have quarter section map, which has the referenced section) and ends at the "True Point of Beginning." 4. From the True Point of Beginning I use the COGO traverse tool again to create a polygon for the property boundary based on the legal description.

If more details about my steps are still needed please let me know, but for now I am trying to keep it simple to avoid boring or dissuading the reader from reading.

Also, for information purposes, this project was given to me to see if it was possible to use GIS to map Legal Descriptions. So far I can't report yay or nay because yes I successfully mapped using a legal description, but no it did not end up where it should. It is very very close, but the boundary I COGO'ed does not cover all the apartments in my building feature class that it needs to. It just needs to move to the south about 100 ft. I am having a hard time believing the legal description is right and our building feature class is wrong because that would mean all the data we have in our database is wrong. I am also not convinced that the legal description is wrong. So that leaves me with thinking I made a technical user error. I can't make any recommendations until I figure out what the issue is and whether it can be fixed.

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Regular Contributor III
I map legal descriptions all the time. My guess is that you have either a mismatched coordinate system or less than accurate data. Many times section data is somewhat approximate as to actual location, especially if it was surveyed a long time ago. Alternately, the legal descriptions could be from a long time ago, and suffer similar problems.

If your data is off by a consistent amount, that would point to a coordinate system difference. I had an issue the other day when a legal description from 1977 didn't line up with our data. The legal description used NAD 1927 State Plane, and we use 1983 State plane, which obviously wasn't available in 1979.

While Arc can project on the fly, if you enter coordinates in 1983, and they're actually from 1927, you won't get accurate results. You could enter the legal in their correct system in a new feature class in a blank map, then add the new feature class to your data. Compounding this, if you have more than one legal description, some could be in one and some in the other. Just some ideas.
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Occasional Contributor II
Is it possible that the discrepancy that you are seeing is the result of using a value of 1 for the "Distance Factor"?  For example, perhaps the distance/bearing information in the legal description were measured in modified coordinates (i.e. - at the ground surface).  If that were the case, I think that you may need to a "Distance Factor" appropriate to your specific geographic location in order to convert it to the State Plane grid. 

I am not sure, but terminology-wise, the "Distance Factor" maybe the same as "Grid Factor" as commonly used in surveying terms.  For example, for our particular site, the grid factor that we use is  0.999763685.  As mentioned above, this value varies depending on your location.

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