looking for a reference scale on a Canadian Chart

[Jim Greer]

Canadian chart #4003, Cape Breton to Cape Cod
The above chart has a scale in the title block of 1=1,000,000 without units. I cannot find a scale like that on a USCG issued chart where one can put his/her dividers to measure distances. Is there something I am missing here????
Thanks

[ItDepends]

I'd be pedantic to point out that the USCG doesn't issue charts... but I get your question.

Anywhere on the chart, one minute of latitude == one nautical mile. Just use the latitude scale on the edge of the chart near your location.

The reason some charts that cover very large areas do not have a distance scale printed on them is that a Mercator project introduces a distortion that makes the distance per inch of paper different at the top of the chart vs the bottom.

This can be ignored on a harbor chart, but is a major issue on an ocean passage chart. I suspect that Cape Breton to Cape Cod is a large enough scale that this is the case.

[Jim Greer]

NOAA issued charts; Anyway, the projection is Mercator on this chart.
one minute of latitude == one nautical mile = 60 nautical mi/degree latitude
The same for longitude?
Thanks

[ChrisJHC]

Originally Posted by Jim Greer

NOAA issued charts; Anyway, the projection is Mercator on this chart.
one minute of latitude == one nautical mile = 60 nautical mi/degree latitude
The same for longitude?
Thanks

Definitely not the same for longitude!

If you look at a globe, you will see that the latitude lines stay the same distance apart as you go north or south.
The longitude lines however, come together at the poles and hence are a different width depending on how north or south you are.

https://www.geographyrealm.com/wp-co...-globe-map.jpg

Always use the latitude lines as your reference!

Note that the difficulty of representing a round object on a flat map causes the latitude lines to be slightly different lengths from the top of the chart to the bottom so try to use the side of the chart to measure distances at about the same latitude you’re in.

Of course, most of this is only an issue when you’re dealing with small scale charts as the effect is insignificant for large scale charts.

[Scorpius]

Originally Posted by Jim Greer

NOAA issued charts; Anyway, the projection is Mercator on this chart.
one minute of latitude == one nautical mile = 60 nautical mi/degree latitude
The same for longitude?
Thanks

Definitely NOT for longitude! One minute of longitude is approximately one nautical mile at the equator but gets smaller as you move north or south - diminishing to zero at the poles.

Take your distance measurement from the scales on the vertical edges of the chart (one minute of latitude equals one nautical mile) beside your course line - not above or below it because, as others have said, the printed size of a nautical mile on a small-scale (large area) chart varies somewhat from the bottom to the top.

[Lodesman]

I've always kind of had a chuckle over American charts putting the distance scale on the chart, when there're two very convenient scales running up the sides. I think it's a holdover from when the lat/lon was depicted in DMS - the separate scale was there to give you cables.