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This page is all about wilderness navigation for hiking, mountaineering and ski touring.

Maps

NTS 1:50,000 map series

NTS Index Map of SW BC

Most recreationists in Canada use the National Topographic System (NTS) 1:50,000 mapsheet series. These maps are convenient scale that covers a large area but also shows sufficient detail.

Each NTS map has a 3 part code. For example: 92 J/3 is the map for Brandywine Falls, the Brew Hut and Rainbow Mountain. The whole country is divided into a grid of 1:1,000,000 scale maps. Southwest BC is map 92 (9 = map index from east to west, 2=map index from north to south). All smaller maps that fit within map 92 are prefixed with the code 92. Each 1:1,000,000 map is divided up into 16 1:250,000 mapsheet that are index with a letter from A-P in a back and forth fashion. Then each 1:250,000 map is divided up into 16 1:50,000 mapsheets that is index with a number between 1 and 16, again in a back and forth fashion. All this is very confusing, so the government has created index maps that show the relationships of the the smaller maps to the larger ones.

NTS maps come in 3 different forms. Usually each map is only available in one form, but sometimes you have a choice

• Tyvek maps are the best. They are printed on Tyvek which is waterproof and highly tear resistant. The only down side is it is very hard to write on them with a pen or pencil. Tyvek maps are a relatively new addition to the NTS map series. The number of maps available in Tyvek seems to be increasing, which is a good thing.
• Printed maps are pretty good. The image quality is the same as the Tyvek map series but the paper is less durable. These maps have been available since the beginning of time.
• Plotted maps are the worst. These maps have been printed on an inkjet printer by a 3rd party map printer and it shows. Image quality is poor and the paper is the same as on the old printed maps. Don't buy these maps if you don't have to.

NTS map contour intervals are 100 feet on the old maps, and 40 meters on the new maps. Bold contours are every 500 feet or 200 meters. The metric maps use the NAD83 Datum (same as WGS84) whereas the maps with contours in feet use the older NAD27 Datum. All maps are marked with Lat/Long around the edges and a 1km UTM grid across the entire map.

TRIM 1:20,000 map series

The BC Government has it's own set of maps that are known as TRIM maps. These maps use the same indexing scheme for the 1:1,000,000 and 1:250,000 levels as the NTS maps. However, the TRIM series uses 100 1:20,000 mapsheets to cover a 1:250,000 map. TRIM maps alway have 3 digits in the 3rd part of the code so that the codes are alway distinct from NTS maps. For example 92 J/1 is a 1:50,000 NTS map and 92 J/001 is a 1:20,000 TRIM map.

The data for TRIM maps is available online through www.maps.gov.bc.ca. This is great for viewing maps but printing you own maps from this is very difficult.

TRIM map contour intervals are 20m, and bold contour intervals are 100m. All maps use the NAD83 datum (which is the same as WGS84)

Latitude and Longitude

The earth is essentially a sphere, so it makes sense to measure your position in terms of angles. Latitude is your north-south position. The equator is 0 degrees, the north pole is 90 degrees north and everything else is somewhere in between. Each degree is divided into 60 minutes, and each minute into 60 seconds (written like this: 49 30'45"N). For convenience, a nautical mile is one minute of latitude.

Longitude is your east-west position, measured from some old observatory in England. Longitude is demarkated in the same way as latitude using degrees, minutes and seconds. The distance between two lines of Longitude varies with Latitude, getting smaller and smaller as you move towards the poles. This makes calculating distances between two points based on their Lat/Long coordinates troublesome.

It is always necesary to specify E or W with longitude and N or S with latitude, although in all of North America it is always N and W, so sometimes the N and W are dropped.

UTM Grid

Most coordinates on maps use Universal Transverse Mercator (UTM) coordinates (an invention of the US military). The Transverse Mercator is one of many map projections that transforms the roundish earth to a flat surface for printing or staring at on a computer screen. The UTM system standardizes the Transverse Mercator map projection by divided the earth into 60 six degree wide numbered zones for the northern and southern hemisphere. Therefore the map should state which zone it is in. Vancouver is in UTM Zone 10N (the 10th zone from the International Date Line).

Coordinates on the map are given as eastings (x) and northings (y). The UTM easting is roughly the distance from the zone’s central line plus an offset of 500 000 m to keep all the numbers positive. Since the coorinates are given in metres on a flat plane, it is generally easy to calculate the distance and direction between two points. In UTM Zone 10, the central line is at -123 degrees longitude. The northing is roughly the distance along the surface of the Earth from the equator. An offset is also added to the northing for zones in the southern hemisphere.

Often guide books (103 Hikes in SW BC) will only give truncated UTM coordinates, instead of the full coordinates to the nearest meter. These may be 6 or 8 digits, with the first half referring to the x and the last half referring to the y.

For example consider the coordinate reference GR946718. Assuming these are given to the nearest 100 m, you can expand the x coordinate to 94 600. If your map has x values running from 464 000 to 500 000 then you know the full x coordinate is 494 600m. Similarly the y coordinate can be expanded to 71 800 and if the maps y values range from 5 456 000 to 5 483 000 you know that the full y coordinate is 5471800m. NTS maps helpfully truncate the coordinates printed on their map grid, so the first two numbers of the truncated UTM x and y coordinates allow you to easily find the 1 km grid you are interested in and the third number is an estimate to the nearest 100m within that grid.

3 different kinds of North

Maps show 3 different north arrows and the relationship between them. True north is the direction to the north pole, and the edges of NTS and TRIM maps are aligned to true north.

Magnetic north is the direction you compass will point. The relationship between magnetic and true north varies with your location and is changing with time.

Grid north is the direction of the UTM grid. The relationship between true north and grid north varies with your location.

Datum

There is no such thing as an absolute location, it is only possible to measure location with respect to some reference point. Latitude and longitude have no meaning if you do not know what the reference point is. A datum is this reference point and maps are constructed by surveying from the reference point outwards.

A datum consists of a description of the shape of the Earth (usually an ellipsoid with a semi-major and semi-minor axis) and information about how this shape is tied to the Earth. Therefore, with a datum, latitude and longitude have a meaning in 3D space (on the surface of the ellipsoid) that can be then located on the Earth's surface.

Longitude is given from a reference point on the surface of the Earth, which is generally Greenwich, England. Latitude is given from the Equator. This is not strictly part of a datum.

Prior to satellite navigation, datums were only fitted to local portions of the Earth (North America for example). Each different part of the Earth used a different datum, and coordinates measured on one datum were not compatible with coordinates measured on other datums. Modern datums (NAD 83, WGS 84) are Earth centred and can be used for measuring coordinates on the entire Earth.

Datums typically encountered in North America are:

• WGS84 is the datum that the GPS system uses
• NAD83 (North American Datum 1983) is essentially the same as WGS84
• NAD27 (North American Datum 1927) is a local datum that was only used for North America. The reference point is Meades Ranch in Kansas[1]. The difference between NAD27 and NAD83/WGS84 is about 200m off in the northing (y) and about 100m off in the easting (x).

For general backcountry travel, it is only important to remember that there is a slight difference between NAD 27 and NAD 83. If you have an old map that uses NAD 27, the coordinates will not match what your GPS displays. You will either have to convert the coordinates to NAD 83, or ask you GPS to display coordinates in the older datum.

GPS

A Global Positioning System (GPS) is a handy device that uses the distance from three or more satilites of known location to calculate your position on the Earth. The functions of a cheap consumer GPS generally include:

• calculating and displaying your location to +-10m (usually UTM coorinates using a WGS84 datum).
• saving your location as a waypoint.
• entering new waypoints.
• calculating the distance and bearing from your current location to a waypoint.
• showing which satellites are available and their position in the sky (used to generate an estimate of the accuracy of calculated coordinates).
• displaying a digital map (newer models).

With a GPS it is generally possible to find locations (ex. huts) in bad weather and whiteouts (when surrouding references needed for compass navigation cannot be seen). Map and compass skills are still important for situations when the GPS decides to go on strike. GPS's tend not to work well when dense forest or mountains are between you and the GPS satellites. The elevation calculated by a GPS also tends not to be very accurate.