Double proportioning - new manual

That's the same language that existed in the 1973 Manual, is it not?

Yes it is one of the more confusing statements in the description. Basically if you follow the procedures the correct result is accomplished.

There is no strange weighting algorythm that is not stated. You need to be sure to figure the cardinal equivalents for all the record courses (the key), compute two single proportion positions on the lines connecting the E-W and N-S controlling corners, and then perform an intersection from those points using cardinal offsets based on true mean bearing.

I don't think the definition changed much from the 1973 Manual but I haven't done a word by word comparison lately. The phrase is used in other proportions also, and I have not succceeded in having make intuitive sense to me.

Corners are selected to control either are or are not control, there is no other weight given to a corner. The distances are weighted in a manner of speaking. But while the record given to corner 80 chains away is twice that of one 40 chains away, those distances as reduced to cardinal equivalents are all given the same weight.

There may be some logic which makes the statement true in that if a corner 80 chains away is found 10 links off of record it affects the proportion a different amount than 10 links in the record to a corner 40 chains away. And that effect is inverse relationship to the distance, but to me that concept is irrelevent to the method of solution.

- jlw

Correct

Joe Webber Sr. had an interesting book about the original surveys
in the Midwest. I saw him and Ben Buckner at an Illinois surveyor
convention. When I explained to them, that the people using the
1973 Manual, were using geodetic north or astronomic north for the
basis of their cardinal direction calculations, they both disagreed.
Cardinal directions were determined according to connecting north-south
or east-west on the ground monumentation in their view.

I read some articles about double proportion by Martin Paquette. He
agreed that cardinal was according to lines determined on the ground
(approximately in north-south or east-west directions.

>Joe Webber Sr. had an interesting book about the original surveys
in the Midwest.

Maybe this one:
• EARLY PUBLIC LAND SURVEYS IN THE NORTHWEST
TERRITORY AND PROCEDURES FOR THE RETRACEMENT
OF ORIGINAL GOVERNMENT SURVEYS IN ILLINOIS by: Joe D. Webber $ 60.00

Found here:
http://www.iplsa.org/pubs.html

Thanks Jerry (and others). I think I may have to track Bob Dahl down to determine why this statement was left in the Manual. I've never understood it...

That is it. One of the interesting things in that book
is that many sections in the north and west tiers of the
townships in SE Illinois did not have closing corners ie the SW corner
of Section 36 and the NW Corner of Section 1.

It is a carry-over statement from the 1973 Manual. This sentence "Each identified corner is given a controlling weight inversely proportional to its distance from the lost corner." is simply a statement of the characteristics of the proportion method. It indicates that corner positions closest to the lost corner location will have more influence on the location of the double proportioned lost corner than those farther away. Just a simple statement of fact. It obviously is apparent that this statement can be confusing, and probably could have been removed from the Manual. Remember though, part of the Manual's purpose is to instruct and educate the Federal interest lands surveyor, so some of the Manual text is an explanation rather than direct direction.

None of these north and west township line corners were made to close under the Surveyor General's Instructions of 1815. There was no such concept over much of the Midwestern PLSS. Just look at Google Earth images of the north and west town lines in northwest Ohio, all of Indiana, all of Illinois, etc.

The farther you get from the Pricipal Meridian, the greater the "jog" you will see in the north lines.