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Plotting Sheet

This is an example of a plotting sheet. These are purchased in large pads from a marine supply store. You may also download a postscript version, pdf version, or fig version if you like for practice purposes, although an 8x11 plotting sheet is a poor substitute for a full-size commercial plotting sheet.

Scroll down for some more information about the plotting sheet.

Compass Rose

The large circle in the center is obviously a compass rose, although it has other purposes as well. The scale of the plotting sheet is (normally) such that the radius of the compass rose is 60 nm = 1 degree.

Latitude Lines

The scale of the plotting chart is such that the distance between the horizontal lines is one degree of latitude. As you can see, the vertical line has been marked in one-minute increments. Also remember that one minute of latitude equals one nautical mile (approximately).

It's a good idea to mark the central latitude line with your working latitude

Longitude Lines

There are no other vertical lines since this chart is intended to be used at any latitude. At the equator, the longitude lines would have the same spacing as the horizontal lines. As you move away from the equator, the longitude lines are drawn progressively closer together.

The first thing you do when using a plotting sheet is to draw in some longitude lines. The easiest way to do this is to use the compass rose as your guide. Starting at the most horizontal points of the rose (90 and 270), count up and down the number of degrees of your latitude. For example, when working at latitude 54, you would count up and down from the 90 and 270 points to find 36, 144, 216 and 324 respectively. Mark these points. Draw two vertical longitude lines through these two pairs. You now have a rectangular-projection map of your local area. Feel free to draw in some sea monsters and mermaids if it makes it look more like a map to you.

See this picture to see a plotting sheet with working lines added for latitude 54.

Scale

This scale deserves some special attention. The plotting sheet is a map, and all maps need some scales. The marks on the central vertical line represent nautical miles (as well as minutes of latitude.) Measurements anywhere on the map may be made by using dividers to transfer distances to this scale.

This scale in the corner is used to measure minutes of longitude. To use, find your working latitude in the scale on the right edge and draw a horizontal line through the scale. Now, minutes of longitude may be measured along this horizontal line.