Monday, May 18, 2015

PLSS CadNSDI – Meandered Water

This is the eighth of a series of documents that describe the contents of the PLSS CadNSDI data set.

Meandered water is NOT hydrography.   These are areas of water that are defined from meander lines of the PLSS, typically as shown on the original Government Land Office (GLO) or recent BLM survey plats. These are not the official representations of coast or water lines and are representations of the lines marked by the survey along the boundaries of meandered water at the time of survey

There is no attribution with the meandered water feature class other than a special survey type code indicating it is water. 

The meandered water is perhaps one of the more confusing feature classes in the PLSS CadNSDI.  The meander lines were run on original surveys to separate the uplands from the water.  In some cases these lines became legal boundary lines and are called out in land descriptions.  In other cases the water’s edge is the legal boundary and the meander line is only an approximation of the water. 

If the PLSS CadNSDI data set originated from digitized USGS topographic quad sheets, which is relatively common I the eastern states, then the meandered water feature is empty, unless a survey plat or local data set has been used to update the original data set.  This is because when comparing the digitized PLSS to survey plats it was noted that hydrography, water captured from a source other than the survey plat, often took precedence over the PLSS meandered water.  In some cases areas delineated as land in the original survey were omitted and in other cases land was extended to meet current hydrography. 

It is critically important that the use of the water boundaries in the PLSS CadNSDI be used as a general reference only and the specific information about basis of land descriptions and the intended representation of water versus upland be well understood for any legal applications.

The graphic below illustrates the many varied ways that meandered water may be presented in the PLSS CadNSDI.

Meandered water
The first thing to note is that the meandered water is “broken” at PLSS Township boundaries.  This means that no meandered water polygon should be larger than a Township.  This makes selecting and working with these polygons more manageable in a GIS.

Notice that the water body in the upper left completes or fills in the “hole” created by the meander in the township, while the meandered water boundaries on the right side are not closed into polygons and do not “fill in” the Township.  The meander line is a boundary not a polygon and as shown in the figure above it may or not be closed to create a polygon.

Also note that for the most part there are no rectangular or special survey features in the meandered water areas.  The meandered water separates the upland and therefore the upland divisions would not be expected beyond the meandered boundary.

There are, of course, exceptions.  In the image below parts of Lots 2 and 3 extended into the meandered water. It is possible that these two lots do end at the meandered water but a corner was added in the lake to compute acreage or to complete a polygon.  In some cases these areas can be changed or updated in maintenance.  The configuration of township lines and meandered water can also depend on the year and season of the survey.

In general meandered water should be identified as a meandered water polygon that is “artificially” divided into a polygons at the Township boundary. 

Water Exceptions
Notice the “inland lake” where the section line is completed through the water.  This is typical for the smaller water bodies.

Lastly, notice that the meandered water is segregated.  This means there are government lots that separate or segregate the meandered water from the upland.  This is also a fairly typical scenario since the regular rectangular polygons would not be sustained around the water bodies.  See the discussion in the PLSS Second Division blog for more information on the lotting. 

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