The Double-Scale Diagram as Map

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Strictly Surveying

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Kent McMillan

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On the subject of maps with scale exaggerated for clarity, it's worth also mentioning old roads. I have in mind one particular county road that at first impression seemed to be completely irregular and unlike the record of its establishment in about 1882 that indicated that the road ran along one straight land grant line and so should also be straight.

When the road was mapped at a scale that exaggerated the offsets from the land grant line to the various points along the right-of-way as used, the pattern was perfectly clear. The chainage stations are in feet, as are the offset distances. This pattern was evident even before the exact location of the land grant line was known and, in fact, helped narrow the search for one particular corner along it. The first version used a trial line as the baseline from which to map the offsets at exaggerated scale, and that led to the ultimate refined version with the line running from corner to corner.

Letter-size pdf from which the above was taken.

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WLineEavesSur.pdf (260.9 KB)

Posted : June 26, 2016 1:32 pm

Kent McMillan

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Just to provide some further discussion of how old markers tend to get buried over time in some settings, here is a pair set about forty-five years apart.

The pole is set up on a drill hole at the center of the 6" x 6" Chalk Limestone seen in the photo below (Elev = 684.01 ft. NAVD88). This is No. 234 on the above sketch.

A 5/8 in. Iron PIpe is 0.85 ft. away (to the left in the photo) (Elev = 684.98 ft.). The Limestone was set in about 1890 (as I recall) and the pipe in 1935, about 45 years later. The pipe was set by a reputable surveyor whose assistants would have known perfectly well what set stones looked like. So presumably the Limestone was buried when the pipe was placed by them, not realizing that the stone remained in place.

A photo showing the relationship of Limestone No.234 to the present road pavement. Yes there is evidence of about four different fence corner posts near the Limestone, all plainly set after it.

Posted : June 26, 2016 7:29 pm

arctanx

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Quick question on drafting a double scale diagram. What is your process for that? Create a block and scale it's x and you axes? What am I missing? I haven't slept much this weekend!

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Posted : June 26, 2016 10:17 pm

Kent McMillan

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arctan(x), post: 379171, member: 6795 wrote: Quick question on drafting a double scale diagram. What is your process for that? Create a block and scale it's x and you axes? What am I missing? I haven't slept much this weekend!

You'd have to rotate the block so that the baseline that offsets are to be taken from is parallel with either the X or Y axis. Then you can scale it.

Posted : June 26, 2016 10:26 pm