Lats & Longs


So if GPS is just a really elaborate system for working out latitude and longitude, where do we go from there?

Honestly, I still recommend that everyone take the time to at least learn the basics of a paper chart. For one thing, if you have raster charts on your chartplotter (don’t worry, I will explain that in the coming days), it is literally just a picture of the paper chart for the same are.

One big difference between paper and electronic charts is that on the paper chart, you can’t miss the latitude and longitude lines, nor the compass rose. On some electronic charts, you can’t see them! While the numbers will eventually start to mean something to you (ie, you can ignore the warship calling out to a boat off its bow because you know that you are miles and miles away from those coordinates), as you are learning the paper charts have lots of tools to help you remember.

So how does a beginner remember which lines run which direction? One way is Jimmy Buffet. When he referred to “Changes in Latitude” he wasn’t trying to get to Europe! A more direct way to remember is that longitude lines are literally long – every single one of them runs from pole to pole. In contrast, the latitude lines that run AROUND the poles are actually quite short. If it helps, learn the British terms: they consistently refer to parallels (latitude) and meridians (aka, the Prime Meridian).

This is important to remember because it means that latitude lines are always parallel to each other. There is a standardized distance between the lines. This distance works out to 1 nautical mile per minute of latitude. There is no equivalent in longitude. these lines touch at the poles and spread out at the equator, so there is no consistency.

On a paper chart, this means that you can use the latitude markers along the side to determine distance. Often, the scale is only listed, not demonstrated, like on a paper land map. But you always have your latitude lines.

Similarly, the compass rose on a paper chart can be a wonderful learning tool for understanding the difference between true and magnetic directions (aka variation). It is literally right there, with a visual representation. No math is required to get the basic concept, although if you have a particularly old paper chart, some math may be required to be entirely accurate.


Be forewarned, a phase out of paper charts in the US has begun. NOAA is now only producing electronic charts, and you will have to request a print out. It is unclear at this point if the production of waterproof chart books will continue. However, these paper charts will continue to be an excellent learning tool, as their shear size allows you to visualize the process of navigation in a way that your tablet does not allow.

Keep safe, keep learning

Tanya Weimer