Wilderness Navigation Guide

Geographic coordinates on maps

2011-04-30T12:20:00.000-07:00

Major latitudes and longitudes are shown as lines across the map or as tick marks in the margins. On most maps or charts, only selected latitudes and longitudes are completely labeled. To prevent clutter, other lines are labeled with partial numbers. For example, only the minutes of arc are shown. The standard way to describe a location with geographic coordinates is to state the latitude followed by the longitude. For example, 46°25'09"S, 105°57'15"E.

For a rough approximation of the latitude and longitude of a location on a map, look at the nearest latitude and longitude lines that surround the location. Visually estimate where the location is relative to the nearest latitude and longitude lines. Take into account that there are 60 minutes of arc in each degree and 60 seconds of arc in each minute of arc.

For more precise results, use a ruler to measure the distance between the location and the nearest lower latitude line, and then measure the distance between the nearest higher and lower latitude lines. Divide the first distance by the second distance to obtain the proportional distance. Convert the proportional distance into angle units and then add the result to the nearest lower latitude line. Calculate the longitude in a similar manner.

Example of how to determine geographic coordinates on a map
On the map below, the proportional distance between Location A and the nearest lower latitude line is 17 mm/38 mm = 0.45. The angular distance between the longitude lines on the map is 1' = 60". Converting from proportional distance to angular units gives 0.45 x 60" = 27". Adding this result to the nearest lower latitude
line gives 53°01'00"N + 27" = 53°01'27"N.

Geographic Coordinate Symbol

2011-03-12T20:34:00.000-08:00

What is Geographic Coordinate Symbol?

After knowing the basic information about the maps, scales, legends, symbols, and also how to measure distances on a map. Now you should know about geographic coordinate system. The geographic coordinate system is a coordinate system that using a set of specified numbers to tag every location on earth. It is one of the two commonly used methods for pinpointing locations on a map. The entire surface of the earth is covered by these coordinate symbols.

Latitude and longitude in a geographic coordinate system.

To specify any location on the globe, you have to find its latitude (parallel) and longitude (meridian). Latitudes and longitudes can be visualized as an array of imaginary lines running along Earth’s surface. A position is measured in angle units: degrees (°), minutes of arc ('), and seconds of arc ("). Each degree is subdivided into 60 minutes of arc, which in turn are subdivided into 60 seconds of arc. Sometimes decimal degrees are used instead of minutes and seconds of arc, or decimal minutes instead of seconds of arc. For example, 156°16'21" = 156°16.35' = 156.2725°.

The latitude of a location is defined as the angle between the equatorial plane and an imaginary line that drops vertically down from the location. This line generally does not intersect the equatorial plane exactly at Earth’s center because Earth’s surface is slightly flattened at the poles. The latitude is a measure of how far north or south a location is from the equator. Latitudes can be visualized as a series of concentric circles centered on the geographic poles and expanding to a maximum radius at the equator.

To specify the latitude, state the latitude angle and whether the position is north (N) or South (S) of the equator. The latitude is 90°N at the North Pole, 0° at the equator, and 90°S at the South Pole. Other locations have intermediate latitudes, for example, 46°25'09"S. The length along Earth’s surface of one minute of latitude is proportional to the radius of curvature along the local surface; it varies from 1843 m at the equator to 1862 m at the poles. The original definition of the nautical mile was the average distance of one minute of arc of latitude along Earth’s surface. Today, the nautical mile is defined as precisely 1852 m.

How Latitudes and Longitudes are Derived

The longitude of a location is defined as the angle, parallel to the equatorial plane, between the location and a reference longitude called the prime meridian. By convention, the prime meridian (0°) is the longitude that runs through an established point at Greenwich, England. From there, other longitudes increase eastward and westward until they meet at 180° on the opposite side of Earth. The longitude is thus a measure of how far east (E) or west (W) a location is from the prime meridian.

Longitudes can be visualized as a series of north-south lines that converge at the poles. To specify the longitude, state the longitude angle and whether the position is east or west of the prime meridian, for example, 105°57'15"E. The length along Earth’s surface of one minute of longitude varies from 1855 m at the equator to 0 at the geographic poles.

How to Measure Distances on a Map

2011-03-11T19:25:00.000-08:00

Use a Ruler, or Curvimeter, or Even Google Maps Distance Calculator.

If you want to calculate the real world distance of a route, you need first to measure the equivalent distance on the map. This step is simple if the route is a straight line between two points. All you need to do is to measure the distance with a ruler. If you don't have a ruler, bear in mind that usually there are inscribed rulers in the base plates of orienteering compasses. Another way is to use drawn grid lines across the maps as measuring tool. The grid lines form an array of identical squares with sides of a specific length. After figuring out the dimensions of one square, the grid effectively becomes a ruler. For more complex routes, divide your route into straight-line segments and measure the distance of each segment one by one. Simply add the length of all segments to calculate the total length of the route.

What if you want to measure a curved path? You ask. Well, you can use a string and put it down along the route. Pinch the string with your finger at the end points of the route then pull the string tight. Measure the length of the string using ruler, or across grid square, and now you can read off the distance. If your map has a bar scale, you can directly know the real world distance by placing the string on the bar scale.

Curvimeter in Use

As a better alternative to measure the distance, you may also use a Curvimeter, a map wheel. It is easier to use even if you are a beginner on reading map, you just set the counter to zero and then roll the wheel along the route and you’re done. The Curvimenter will show the accumulated distance. Pay attention to the units as the curvimeter can either directly display real world distances for maps of certain scales, or just show the actual distance on the map.

Scale of a Map

2010-11-03T04:11:00.000-07:00

Three Types of Map Scale.

All maps or charts are drawn to a specific scale. The scale is the relationship between a distance on the map versus the same distance in the real world. A large-scale map shows a small area in great detail, while a small-scale map covers a large area but with little detail. Selecting a map with an appropriate scale is therefore a compromise between coverage and detail, and depends on your intended activity. For example, climbing a mountain with complex topography requires a large-scale map, while a small scale map may be a better choice for a long canoe trip. The scale that you see written on the map is just an approximation. It is never completely constant across the whole map, but varies according to the projection that was used to create the map. The larger the area that a map covers, the more susceptible it is to scale variations. The scale can be expressed as a verbal scale, a ratio scale, or a bar scale.

Verbal scale
A verbal scale uses words to express the relationship between a distance on the map and the corresponding distance in the real world.
Example of verbal scale
The following is written in the margins of your map: “4 cm on the map represents1 km on the ground.” Here it is implied that a distance of 4 centimeters on the map is equal to 1 kilometer in the real world. This relationship allows you to calculate any other real world distance from the map. For example, a measured distance of 15.6 cm on the map represents (15.6 cm)/(4 cm) x 1 km = 3.9 km in the real world.

Ratio scale
The scale of a map can be expressed as a ratio between a distance on the map versus the same distance in the real world. Some people find ratio scales confusing because distances are not tied to a specific unit. You can use any unit you want as long as you stick to the same unit during the conversion between map and real world distances. After doing the conversion, you can of course convert the resulting distance into other units.
Example of ratio scale
A map with “Scale 1:50 000” written in the margins means that the distance between any two points is 50 000 times longer in the real world than on the map. For example, a distance of 8.5 cm on the map would be 50 000 x 8.5 cm = 425 000 cm = 4250 m = 4.25 km in the real world.

Bar scale
A bar scale shows real world distances directly on the map. Bar scales is the most common type of scale, and are easy to understand because of their graphical nature. A common practice is to show several bar scales on the same map, each representing a different length unit. Bar scales are often shown together with ratio or verbal scales.
Examples of bar scales

Bar-Scale

Map Legend Symbol

2010-11-01T20:32:00.000-07:00

Never Use a Map Without Knowing Its Symbol and Color's Meaning.

The map legend shows the meaning of the colors and symbols on your map. These symbol are very important in navigation. Unfortunately, there is no worldwide standard so the colors and symbols may mean different things on different maps. This is why it is important to consult the legend before using a map from an unfamiliar series.

Colors
Since there are only a few colors to choose from, colors normally show entities that cover significant portions of the map. For example, vegetation zones are shown in green, bodies of water in blue, glaciers in white, urban areas in red, and areas with little or no vegetation in brown.

Symbols
Map symbols are graphic representations of natural and man-made features. Point features such as campsites, lighthouses, or survey markers are shown as single symbols. Linear features such as roads, trails, power lines, railway tracks, rivers, or political boundaries are shown as dashed or continuous lines. Areas such as swamps, moraines, tidal flats, or sand dunes are shown as groups of identical symbols. Symbols are almost always shown at an exaggerated scale. Otherwise, they would be too small to be visible on the map.

Introduction to Navigation

2010-10-31T22:53:00.000-07:00

Welcome to Wilderness Navigation Guide.

Navigation is both an art and a science, requiring creativity as well as raw technical skills. It has always been an intricate part of human activity. In the past our very survival may have hinged on using natural navigation clues to find a decent food source and then retrace the route back to the cave. In stark contrast, present-day navigation systems can guide an aircraft across oceans and continents to a perfect landing in zero visibility. Future space travelers will no doubt use devices that are even more sophisticated.

Despite these technological advancements, we often find ourselves frustrated by navigational tasks. Just ask anyone who has tried to find his or her way out of an unfamiliar city.

Studies have shown that having a general sense of direction is closely linked to the ability to mentally rotate objects. This may explain why some people easily become disoriented while others have seemingly no trouble finding their way. The widespread belief that some people, especially members of indigenous groups, can navigate purely by instinct is however a myth. Wherever you are on Earth, you are likely surrounded by clues that you can use for navigation. It isn’t so much an innate sense of direction that differentiates navigators, but rather the ability to recognize navigational clues and put them to effective use.

The introduction of the global positioning system (GPS) and the availability of low cost GPS receivers has revolutionized navigation. Travel during poor visibility and through terrain devoid of landmarks can easily be done by anyone willing to put their trust in instruments. Then again, overreliance on technology is also a sure way to get into trouble. High-tech gadgets have a tendency to fail at the worst possible moment, and you may suddenly find yourself navigating like your ancestors.

Except for a chapter on emergency communication, this book is strictly about navigation. It does not deal with wilderness survival, route finding, or the sport of orienteering. The aim is to take away the mystique of navigation by explaining all the essential tools and techniques. If you are a raw beginner, concentrate on learning how to navigate with a map, compass, altimeter, and GPS receiver before diving into topics such as celestial navigation. If you are already a competent navigator, this book will almost certainly give you a deeper understanding of how things work, and more importantly, why things sometimes don’t work.

An earnest attempt was made to present the material in logical order and avoid disruptive references to previous or subsequent sections. Unfortunately, this had to be balanced with keeping distinct topics together, and avoiding excessive repetition. No attempt has been made to separate basic from advanced topics. If you get bogged down, skip to the next section and return later to the material that you found challenging.