Map Systems

This page explains the map systems on the TowerBells Website, answering the following questions about them:

The answers appear below, in the same order as those questions.

What kinds of maps are there?

There are two kinds of maps on this Website, as follows: (We cannot show all of the sites in the world at once, because there are so many that the response time for drawing the map would be much too long.  Besides, it would be much too cluttered to be useful.)

Why aren't maps embedded in the pages to which they are related?

There are three reasons for this:

What are the characteristics of each kind of map?

The common characteristics of both kinds of map are as follows: The distinguishing characteristics of the two kinds of map are as follows:

How are the regional locator maps organized?

The regional locator maps are organized into six independent sets, as follows:

Regional locator map sets can be entered directly at any sub-region.  This is convenient for connecting them to various index pages without losing access to the entire set.

How are varying levels of location accuracy handled?

Accuracy has to do with how precisely you know something, while precision has to do with how well you can specify what you know.  For a location of the surface of the Earth, measured in decimal degrees of latitude and longitude, this is roughly as follows:

Precision Example Maximum error
Whole degree 9. +/- 30 nautical miles
+/- 55.56 kilometers
0.1 degree 9.8 +/- 3 nautical miles
+/- 5.56 kilometers
0.01 degree 9.87 +/- 0.3 nautical miles
+/- 556 meters
0.001 degree 9.876 +/- 0.03 nautical miles
+/- 55.6 meters
+/- 180 feet
0.0001 degree 9.8765 +/- 0.003 nautical miles
+/- 5.56 meters
+/- 18 feet
0.00001 degree 9.87654 +/- 0.0003 nautical miles
+/- 0.556 meters
+/- 1.8 feet
The accuracy specified in the last column applies strictly to measurements of latitude.  For longitude, it is correct only at the equator; the maximum error shrinks progressively as one moves toward the poles.

Generally, we use five decimal places when we are confident of placing a map pin on the part of a building or structure that contains the bells, four places when we know only the property, three places when we know only the town, and two places when we know only the country.  Someimes we use one more decimal place than is strictly justifiable, simply to place a map pin nicely.

Answers to questions you didn't think to ask?

If you've read this far, you might as well read the rest!

Here's a bit of history:  When the author began collecting carillon information, around 1960, all that was needed to identify a carillon on an index card was the city, state and institution name.  When computerization of the collected information was begun, in the 1970s, it made sense to include the latitude and longitude of the city, as found in printed gazetteers of the day; those values were specified in degrees and minutes.  After the software was converted to run on a personal computer, in the late 1980s, a database of geographic boundaries was acquired, on a set of floppy disks.  But while the existing city locations would have worked well with this geographic database, the time constraints of earning a living and raising a family did not permit development of a mapping system adequate to utilize it in combination with the author's data.  In the late 1990s, when the first version of a Website for the GCNA offered the opportunity to publish the author's data online (see the Website history), it was quickly discovered that there existed free online mapping services that could serve this need.  However, proper placement of sites that were accurately known required more precision than was available using just degrees and minutes, so we began stating GPS coordinates as part of the Location section of site data pages.  (For the complex history of actually utilizing that information, see our Map Service History.)  Now we also include GPS coordinates in the descriptions of independent great bells (when we can).  Continue with the answer about locarion accuracy, above.

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This page was created 2019/05/11 and last revised 2019/05/13.

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