SouthWestern Quebec Placenames


Notes regarding
Latitude/Longitude Coordinates


Source of Lat/Long Data

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Most of the entries in this Compendium of place and feature names have Latitude and Longitude coordinates listed in addition to ordinary map references. All of the coordinates were obtained using Microsoft Streets & Trips 2001 computer mapping program.

This program is the first reasonably priced computer map for Canada that is accurate and shows details down to street level. The Lat/Long coordinate readout is very accurate in reference to the roads (this has been verified using a GPS satellite receiver). On the negative side, the depiction of rural areas is poor - roads are not named except for numbered highways and the names of the towns that are named are often misplaced. Water features such as rivers and shorelines are either non-existent or bear little recognition to reality. It is hoped that future versions will be better. (So far, Streets and Trips 2002 is no better in regard to rural information but the 2005 version does have rural road names and other features.).

The Latitude and Longitude is displayed in Decimal Degrees, rather than the more common Degrees, Minutes and Seconds. The Decimal Degrees can be converted easily to minutes and seconds using a simple calculation. Simply multiply the decimal portion of the degree reading by 60 to get decimal minutes. Multiplying the decimal portion of the minutes by 60 will give seconds. For example take 45.211 degrees. Multiply .211 by 60 and you get 12.66 minutes. Multiply .66 by 60 and you get 39.6 seconds. So 45.211 = 45 degrees 12 minutes 40 seconds or 45°12'40".

The MS Streets & Trips Lat/Long readout has a resolution of 5 decimal places but I have rounded the listed reference to the nearest 3 decimal places which in our area represents about 100 metres except for large features such as townships, counties etc which I have rounded to 2 or 1 decimal place as needed. Sufficiently precise for our purposes.

The Lat/Long Coordinate readout is only as good as the placement of the markers. I used existing modern roads as the reference to placement of the markers. Roads generally fall into 3 categories that can greatly affect the accuracy of placement.

Hamlets are not a problem to locate but larger entities can present location problems. Villages and towns are either marked at their town hall, at a significant crossroads or other geographic feature, or generally in the center of the town. Cities, townships, counties and other large features are generally marked at the approximate center of their area. But the location is only approximate and should be considered as so when making measurements such as distances to other places.

Roads, concessions and other long thin entities are located at their approximate center or some other point that is not in conflict with neighbouring features. Rivers and streams are located by their mouth and often at their source as well.

Resolution, Precision and Accuracy

These three technical terms are often mis-understood by laymen. For those, who do not have the benefit of a scientific or technical background, let me explain the difference between them.

 
Resolution

Resolution is a measure how small a reading is subdivided. If a digital reading has 5 digits, then it has a resolution of one part in 100,000 (00000 to 99999). A reading that has a resolution of 5 digits does not mean that it is precise or accurate to that value. In fact, all it means is that the display you are reading has 5 decimal numbers showing, nothing else. Precision can never be better than resolution but it is usually a lot worse.

 
Precision

Precision is the measure of the repeatability of your reading. If you take 100 readings of the same measurement, there will be a variation in the readings. The smaller the variation or range of readings, the better the precision. In the case of the Streets & Trips map, the precision is a bit better than 3 decimal places hence the decision to round to 3 decimal places. Does this mean that the readings are accurate to 3 decimal places? Not at all. Accuracy is not related to precision except that precision will put an upper limit on accuracy.

 
Accuracy

Finally we come to accuracy. Accuracy is the variation between the measured readings and the true value of the measurement. For example, I can place a location pin on a map and measure the Lat/Long coordinates 10 times. The readings will probably be within a thousandth of a degree (3 decimal point precision). But the accuracy of the reading will be dependant on the interpretation of where the pin should be placed, the accuracy of the reference point to which the reading is compared and the accuracy of the measuring device. I may place the pin in a spot and be able to take readings that are precise to 100 metres but maybe I placed the pin 5km from the true location of the feature or maybe the measuring device is not calibrated and is 10% in error. The accuracy in that case would only be at best +/-5km. Accuracy can be no better than precision but it can often be a lot worse. Unless you understand the underlying errors in the measurements, your reading can often be misleading.

I hope that this explanation has clarified the science of measurement a little.

As indicated above, I have rounded all readings to 3 decimal point precision. This corresponds to +/-100m. The accuracy is another matter, but at least it will get you into the general area where the feature is located. In cases of features that are larger, such as concessions, or larger towns, I have rounded the reading to 2 decimal points corresponding to a precision of +/-1km. In some cases, the Latitude reading is required to be more precise that the Longitude (or vice versa) to avoid confusion with long narrow features. For really large features like counties, I have rounded to 1 decimal point which corresponds to +/-10km.

Computer map file available

I have prepared an accessory Streets & Trips data file that shows most of the Lat/Long referenced place and feature names in this document. I will make it available to anyone who has the Streets & Trips program so that they can easily find the named places on the map. If you are interested in obtaining an up-to-date copy of this file, e-mail me and I will forward a copy as an attachment. It is a 400K file but when zipped is only a 100K file.


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©copyright 2001-7 Burton Lang Rev:2007/02/04