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Date first written: 2015.12.03 Last Review: 2016.07.21
When planning the documentation of road and trail networks, it is handy to have some fixed and unchanging way to refer to key junctions, even if the road layout or names change. To do this, we have short two digit "junction codes" for all key junctions. The junction codes are generated directly from the lat-long, and thus don't change even if the road network changes. The junction code is made up of the second decimal place of the latitude, and the second decimal place of the longitude. for example:
The point where you turn off the White River main
and cross the river
In the above, note that the "7" is the second decimal place of the latitude, and the "4" is the second decimal place of the longitude.
- How specific?
How specific are these junction codes? A given junction code is specific to an area about 1 km square. (Since one degree is 111 km, the second decimal place of a latitude is 1.1 km.)
- How often do they repeat?
The first decimal place of latitude covers 11.1 km. So there will only be one jct 74 within a 11 km square. Is that good enough, given that the area of discussion could be 20 km square? Yes, the short codes are sufficient, because in a typical discussion, you only have less than a dozen key junctions, and so it is very unlikely that you will have two Jct 74 in the same discussion. In practice I have yet to have a case where I have duplicate junction codes in the same discussion.
In road plans, it is handy to make a list of
One example is in Tetrahedron Plateau Trail Naming Plan
(Junctions within same km)
When multiple junctions are less than 1 km apart, they will sometimes have the same junction code. Sometimes, I distinguish them by using a letter such as "W" or "E". Eg: Jct 74e and 74w. For example, the Chance-Tricouni Connector has several duplicate junctions.
In other cases, we can distinguish two junctions by adding another level made up from the third digits. Eg: In Roberts Creek area I have 75-09 and 75-83. In that case, the extra level is preferred to "n" and "s" because those two junctions are quite separate.
The "distinguishers" are only necessary where there are collisions. In the rest of the pan, we just stick to 2 digit junction codes. See Elphinstone Plan
The delimiter for two levels should be distinct from the way roads are named. Could use dot Eg: 75.09 or slash 75/09. Or colon 75:09.
The "dot" is easy to say, and the decimal idea more or less suggests "refinement". The key concept is "subdivision".
- In waypoints
Whenever I'm digitizing a road, I put in the junction number for every significant looking junction, even if we may not actually digitize the other road. The keyword is "Jct", and then you read off the lat-long. Eg: Jct 26
- In Junction dictionary
These junction codes can then be listed in a "junction dictionary" in the road plan document.
- In Emails and discussions:
Note: Junction Codes replace "Exit numbers" or any sequential numbers such as were used on Mamquam Main.