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<p>Hello.</p>
<p>I have a question about MGRS or USNG grid line labels, and how many principal digits should be used.</p>
<p> </p>
<p>The background is that the line label is based on the UTM easting or northing for the line, which is a 6-digit or
</p>
<p>7-digit number. But only the five last digits would be used in MGRS or USNG notation, so the fifth digit from the
</p>
<p>end is the first principal digit, and is written with a larger font than the leading or trailing digits. So far, so good.</p>
<p> </p>
<p>Here is my confusion. In the Military Map Reading 201, <a href="http://earth-info.nga.mil/GandG/coordsys/mmr201.pdf">
http://earth-info.nga.mil/GandG/coordsys/mmr201.pdf</a> ,</p>
<p>examples show that when the grid line spacing is 10 000 m, there is one principal digit in each line label,</p>
<p>and when the grid line spacing is 1 000 m, there is two principal digit in each label. There are no examples<br>
for larger scale maps, but my extrapolation has been that there would be three principal digits when the line<br>
spacing is 100 m, four principal digits when the line spacing is 10 m, and five principal digits when the line
<br>
spacing is 1 m. (The basic idea is that the trailing digits are all zeros, with as many trailing digits as possible.)</p>
<p> </p>
<p>However, I recently found a style guide for USNG (which is nearly identical to MGRS),</p>
<p><a href="http://www.floridadisaster.org/gis/usng/Documents/USNG_style_sheetV1-11plus.pdf">http://www.floridadisaster.org/gis/usng/Documents/USNG_style_sheetV1-11plus.pdf</a> ,</p>
<p>which simply says that there are always two principal digits in a line label. Examples are given for
</p>
<p>many line spacings, including 10 000 m. (The basic idea must be that when reading the principal digits
</p>
<p>as a number, you get a value in kilometers.)</p>
<p> </p>
<p>The two documents clearly contradict each other for the case with 10 000 m line spacing. But I am</p>
<p>not sure if my extrapolation of the military convention to dense line spacing is correct - maybe the
</p>
<p>military convention is to have one or two principal digits, but never more than that.
</p>
<p> </p>
<p>I would like to get comments or opinions on this, since I am currently working with MGRS grid visualization.
</p>
<p> </p>
<p>Best regards,</p>
<p> </p>
<p>Mikael Rittri</p>
<p>Carmenta</p>
<p>Sweden</p>
<p><a href="http://www.carmenta.com">http://www.carmenta.com</a></p>
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