posted on May, 4 2019 @ 03:56 PM
On the subject of maps...Want to hear something scary?
I work in aviation, and in the world of airports there is a document called an Airport Layout Plan (or ALP). This is a critical document which shows
where everything is located at an airport...exactly. Everything at an airport is based on this document, including the approach paths for aircraft,
the locations of taxiways and runways...everything. If something gets built at an airport it must, by law, be shown on the ALP. This prevents
'trivial' things like planes flying into buildings and the like.
Navigation aids around the country are way points on the ground which aircraft can use to determine their exact location in the air.
Over the years, all of these things have been located using traditional land survey methods, the same methods which mapped out this entire country,
and the world around us. This, back long before there was ever a GPS constellation system. Land survey was an imperfect science / engineering
discipline because, well, the Earth is round. Have you ever been driving down a long straight country road when all of a sudden it makes a quick jog
to the left and then back to the right again? We all have. This is an example of survey errors over the years. Cities and towns are no different,
just like airports. Without going into a whole lot of detail, errors get pushed out to locations where they don't really matter so everything can
remain referenced correctly to certain points of reference within a system (i.e. a City, town or airport). The errors get corrected out in some
distant location where they don't matter as much. Imagine if an airport runway made a 200' jog to the left and back to the right again! Bad ju-ju,
Now enter a thing called GIS, or Geo-spatial Information Systems. These are computer software systems which show where things are. They're like a
big brother to things like Computer Aided Design (CAD). The idea is to create maps which show where everything is, but now those errors we spoke of
earlier matter...and they have to be corrected...all of them!
Back in 2007 the FAA decreed they were moving toward what is known as an "e"ALP, meaning an Electronic ALP. Okay, but where would they get the data?
Well, the thinking is, from GIS systems. But where did all the GIS systems get their data? Most of it comes from the original land survey data, but
not all of it. Some of it comes from modern GPS survey data. The problem is, the land survey data deviates from the GPS data. To draw a crude
analogy; it didn't matter if the airport was 200' off of where it was supposed to be (just an extreme example), because anyone flying into the airport
knew where everything else in the vicinity was. But now, when you take that same data and plug it into country wide GIS systems to make your eALPs
from these errors matter...big time! And, something has to give!
Re-surveying an entire airport can be a monumental undertaking, and take years to complete. Yet, in the meantime, the eALP exists, but the airport
isn't exactly where it says it is. It may be just a foot, but in some cases it can be 20' feet, or even a 100' feet. Now, fortunately this problem
was known, and the locations of things like runways and such were corrected immediately. But there are still compounding errors in other areas at
airports which will not be corrected for years, if ever.
Technology is great...sometimes.