LOP plotting question

[Rumata]

Rumata,

Can you explain what that means?  

Thanks,

Fred

Gentlemen, below is the long citation from Mixter which explains , I hope, the method

"...Place the paper with the ruled lines vertical. Near the lower edge draw a horizontal line to represent the parallel of lattitude (let's make a plotting sheet for a small area  north and west of 35 deg. N, and 70 deg. West) 35 deg N. Near the right-end of this selecta point where it intersects a vertical line and label the point  35 deg N and 70 deg. W. Westward, to the left, label each 10' of longitude and blacken the vertical lines which represents the meridians through these points. The ruling of the paper may indicate that the space between the vertical lines should represent 2' or 3' of longitude. Avoid a scale of less than 1/8" per 1' of longitude.

To complete a plotting sheet, parallels of lattitude must be drawn. As it is a Mercator projection, the lattitude scale will be greater than the longitude scale, the increase depending on the lattitude. To locate the 10' parallel, draw a line from a point on the parrallel already drawn, such as 70deg30' W, with the line making an angle with the horizontal equal to the latitude, or 35 deg.N in this instance. The length of this line between the vertical lines labeled 30' and 20' is the required space between the 0' and 10' parallel and the 10' parallel is drawn accordingly.

For practical purposes the same spacing may be used to draw the parallels of 20' and 30', or any other 10' interval within 1 deg of the lattitude used as the angle for drawing the diagonal line. When marked at the points where it intersects each vertical line, the diagonal gives the scale of latitude or distance for use anywhere on the plotting sheet. ..."

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Fred_BRumata,
Can you explain what that means?  
Thanks,
Fred

I think what he means, Fred, is that if you take a compass rose and make (for example) the radius one degree at the equator, then draw a diagonal  (hypotenuse) to any degree up from 90 (say 45 degrees) from the rose center to the circumference edge, and then draw a vertical line down from that point to the 90 horizontal line where it and the line you just drew (side opposite) form a right triangle, the line length along the side adjacent (90 degree line) then represents the scale of longitude (one degree) at 45 degrees north or south latitude on the globe....  For me it is more entertaining to use this method to scale longitude than to use the curved lat/long scale associated with all printed work sheets where the scale is drawn for you.  You may then also take any length in minutes (and seconds if the scale is sufficiently large) .   I did my best... :) 

I always assumed that if a measurement in nautical miles or knots (say boat speed) is required, I use full knots as measured along any great circle line of longitude irregardless of latitude; but if a measurement is called for in degrees, minutes, and seconds (such as in the trig) I then use the method described above to ascertain the length of degrees of longitude at higher latitudes.  I hope this made sense.
joe

Gentlemen, below is the long citation from Mixter which explains , I hope, the method

"...Place the paper with the ruled lines vertical. Near the lower edge draw a horizontal line to represent the parallel of lattitude (let's make a plotting sheet for a small area  north and west of 35 deg. N, and 70 deg. West) 35 deg N. Near the right-end of this selecta point where it intersects a vertical line and label the point  35 deg N and 70 deg. W. Westward, to the left, label each 10' of longitude and blacken the vertical lines which represents the meridians through these points. The ruling of the paper may indicate that the space between the vertical lines should represent 2' or 3' of longitude. Avoid a scale of less than 1/8" per 1' of longitude.

To complete a plotting sheet, parallels of lattitude must be drawn. As it is a Mercator projection, the lattitude scale will be greater than the longitude scale, the increase depending on the lattitude. To locate the 10' parallel, draw a line from a point on the parrallel already drawn, such as 70deg30' W, with the line making an angle with the horizontal equal to the latitude, or 35 deg.N in this instance. The length of this line between the vertical lines labeled 30' and 20' is the required space between the 0' and 10' parallel and the 10' parallel is drawn accordingly.

For practical purposes the same spacing may be used to draw the parallels of 20' and 30', or any other 10' interval within 1 deg of the lattitude used as the angle for drawing the diagonal line. When marked at the points where it intersects each vertical line, the diagonal gives the scale of latitude or distance for use anywhere on the plotting sheet. ..."