CENTERLINE OF PRISM…MAP LABEL?Posted by fls on January 31, 2012 at 4:07 pm
I just picked up a 1926 map from the clerk’s office and it has a line labeled as “centerline of prism”. It is shown as a 5′ offset line to a property line denoting a 5′ reservation to a Village. It could have something to do with a abandoned canal.
What is centerline of prism????
- 10 Replies
- MemberJanuary 31, 2012 at 4:15 pm
the canal prism is the cross-section of the canal, so I image its the centerline of that cross-section
- MemberJanuary 31, 2012 at 4:21 pm
Just off the top of my head, it “sounds” like the mid-point of a LINE from catch-point to catch-point of the construction prism. So on a through fill (road) it would be toe-toe of the fill. On a sidecast (dugway) it would be toe (fill) to top of back (cut), and so forth and so on. In the case of a ditch, it “might” be toe-toe of the fill on each side of the ditch (assuming that is how it was built). It would NOT necessarily be the centerline of the ditch per se, but it would be the centerline of the “disturbed” area, which does (kinda) make sense (to me anyway).
- MemberJanuary 31, 2012 at 4:22 pm
The math definition of prism is “a polyhedron having parallel, polygonal, and congruent bases and sides that are parallelograms”.
It may have been used to describe the 5ft parallel line.
- MemberJanuary 31, 2012 at 5:06 pm
Then, it very well could be the centerline of the abadoned canal bed???
- MemberJanuary 31, 2012 at 7:22 pm
I believe Loyal has it correct. Its the centerline of the disturbed area, catch point-to-catch point (toe of fill or top of cut) on each side. It’s not the same as the flowline or centerline of the ditch.
- MemberJanuary 31, 2012 at 7:42 pm
Here’s a couple of interesting links:
The second link has a section thru the original Erie, which I believe may have been standard for NY canals of that period. However, the contrary may be shown……
I’ve worked near abandoned canal beds and have always treated center of prism, when called for in a conveyance, as center of the canal bed proper, ignoring the towpath and opposite berm.
- MemberJanuary 31, 2012 at 8:19 pm
Your canal may vary…
Colloquially “prism” is used around here to define the area between the tops of bank, but based on research I did a few years back for National Park Service scenic easements adjacent to the C&O Canal, the “prism” is the cross-sectional area of the flooded portion of the canal when filled to it’s design depth. It’s often designated on plans by “top width x depth x bottom width” (for example, the design prism for the C&O Canal was 60x6x48).
- MemberFebruary 1, 2012 at 2:07 am
Yes, Caltrans says they have the entire roadway prism on prescriptive highways, not necessarily a uniform width.
- MemberFebruary 1, 2012 at 1:42 pm
I think the best course of action is to find the canal maps and see what they have to say.
- MemberFebruary 2, 2012 at 1:55 pm
canal may vary…
Great Links Sergent thank you
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