GPS Instant Navigation
Second Edition

Published Reviews

Accurate in an "Instant"

"GPS Instant Navigation" is aptly described in its title. The book is intended as a tool for skippers, who can use it to plan route selection, plot waypoints and adapt them to electronic charting.

Written by Kevin Monahan (a Canadian coast guard officer with over 20 years’ experience) and Don Douglass (a longtime cruiser of the Northwest) this reference book starts with basics of navigation and leads, chapter by chapter, to more advanced concepts and techniques. The book touches on waypoint realization, understanding GPS accuracy and navigating using differential GPS (DGPS).

Information in the book is so current that it even touches on the U.S. Department of Defense’s removal of selective availability in May of this year. The book retails for $29.95.

Readers' Questions


I wonder if you could answer a question for me. I have been trying to pinpoint some spots on a topo map but the reference numbers (long/lat) I have been given I don’t understand, e.g. 50.075 N, 125.742 W. The positions are on land and I assume it (degrees/minutes/seconds) works the same way as on the ocean. The numbers I found were on the web site:

I have the book "GPS waypoints, British Columbia Coast" but it could not help me on this matter. Hope you can,


Dear Adam,

The coordinates from the web-site you visited are expressed in decimal degrees. You ar probalby most familiar with positions in degrees, minutes and seconds. To convert decimal degrees to degrees and decimal minutes, you simply multiply the portion of the latitude (or longitude) after the decimal by 60. For instance 50.075N becomes 50 degrees plus (0.075 x 60) = 4.5 minutes. The latitude then reads 50 degrees 04.5 minutes (or 50 degrees, 04 minutes, and 30 seconds).

However, when you try to plot the position on the topographical map you will most likely encounter difficulties because the map probably uses Universal Transverse Mercator (or Military) grid coordinates, which use Northings and Eastings. Our book "GPS Instant Navigation (2nd Edition)" discusses UTM on page 48.

Check the topo map again to determine if it is marked with degree or minute ticks in the margins. In most cases topographical maps will only show whole minute ticks in the margins--they normally do not show the parts of a minute of latitude or longitude, so you will have to interpolate to estimate the proper position.

The US Army Corps of Engineers has posted a free program which converts between various coordinate systems. You can obtain it at or you can perform the conversion using a GPS receiver. Simply enter the lat/long co-ordinates as a waypoint, and then change the display from NAD 27 (or NAD83) to UTM coordinates. You should then be able to read the UTM coordinates of the waypoint directly from the GPS
Thanks for you inquiry and good luck.

Kevin Monahan

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