# Target Title

Donald Kenney (donaldkenney@gmail.com)
Last Update: Tue Jan 19 19:57:07 2021

# Introduction

## Accuracy of values with various numbers of fractional digits

Approximate accuracy of Longitude for various precision of degrees (Latitude will be 25-50% more accurate)
Number of fractional digits Latitude- Accuracy(meters) Latitude- Accuracy(feet) Longitude-Accuracy 30degN(meters) Longitude-Accuracy 60degN(meters)
1 11.112km 6.9047mi 9.622km 5.555km
2 1.111km 3646ft 966m 556m
3 111m 364.6ft 96.6m 55.6m
4 11.1m 36.5ft 9.66m 5.56m

1. The accuracy of Longitude is roughly the latitude value multiplied times the cosine of Latitude.

2. Some sources give positions to 5, 6 or more fractional digits. I suspect that the positions encountered in day to day map work without surveying are rarely accurate to even four digits.

## Codes used in the Lat-Lon Field

Over the years, I've used a number of different codes in the location field. I'm slowly converting them all to something along the line of Axxxy where xxx consists of one or more letters of numbers followed by one digit 0-5 that is the GA- digit described below. A question mark is appended if I think the location is very questionable. The xxx code is generally three characters, but can be more or less. The letters look forward to a day when there will be individual site pages for each page. Upper Case letters indicate road maps, lower case letters indicate terrain maps, numbers indicate satellite maps. The higher the letter/digit, the smaller scale the map.

e.g. a code of AIm73 indicates a road map at about 12 km to the inch, terrain map at about 1500 meters to the inch, a satellite map at 150m to the inch and my guess (the final digit 3) that the latitude longitude is within 10km of the actual site.

A code in the form of GA0 through GA5 is provided with my guess as to the actual accuracy of the positions
 GA0 Very likely dead on. Go there and look around GA1 Probably within a few minutes walk GA2 Probably within 2 or 3 km GA3 Probably within 10 km GA4 Probably within 50-60 km GA5 Very likely on the correct planet

## Field 14, Processed, Nearby Sites

An asterisk in field 14 indicates that I've looked at the location on a map and it is probably as reasonable as it is going to get. If a string of site IDs follows the asterisk, they are the IDs of nearby/duplicate sites. As a May2015, about half of the site locations have been reviewed, and the duplicate/nearby site info is very sparsely populated. Software to help spot duplicates may get written when and if I finish the tools for cleaning up the fossils field.

## MAP Coordinate Systems

A number of different (often incompatible) coordinate systems are or were in times past used to identify locations. I use latitude/longitude with the (near) universal convention that latitudes are positive north of the Equator and East of the Greenwich Meridian. Since (almost) all my North American sites are West of Greenwich and North of the equator, (almost) all locations will consist of a positive latitude and a negative longitude.

There are other systems that may be encountered if you use other sources -- which I recommend doing -- as well as my lists.

### PLSS (Public Land Survey System)

A system used to identify property lines in states West of the original American colonies. It is based on six mile by six mile grids relative to rather arbitrary baseline latitudes and meridians. Because the PLSS grid is printed on US topographic maps it has been used for much of the 19th and 20th centuries to identify map locations. Unfortunately, it is less than ideal for that purpose. See PLSS.HTM

### DLS (Dominion Land Survey)

A system somewhat similar to the US PLSS, used in Canada to survey the Prairie Provinces (Alberta,Saskatchewan,Manitoba). See PLSS.HTM

### UTM (Universal Transverse Mercator

A relatively modern grid mapping system dating to the 1940s. It is based on (mostly) 6 degree wide longitude zones with offsets North and East of the reference point given in meters. See https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system

### Carter Coordinates

A system thankfully used only in Kentucky for identifying the location of oil and gas wells and sometimes rock outcrops. It is based on a grid of 5 minute by 5 minute squares identified by letters (A ... Z, AA ...) and numbers. Within the grid square, positions are specified as feet East and South of the Northwest corner. See http://www.uky.edu/KGS/emsweb/kyogfaq/kyogfaq9.html

Copyright 2021 Donald Kenney (Donald.Kenney@GMail.com). Unless otherwise stated, permission is hereby granted to use any materials on these pages under the Creative Commons License V2.5 see http://creativecommons.org/licenses/by/2.5/.