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Chapter 13

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Western University
Geography 2122A/B
Micha Pazner

Chapter 13 Position Finding and Navigation Orienting the Map  Orient a map means to determine how directions on the map align to directions on the ground.  Before maps were drawn with China on Top, but now made using True North at the top  Inspection Method o Easiest ways to orient map – inspection method o With this technique, do not need to know which way north is. o No need of tools. Only 2 conditions need to be met:  Must be able to see one or more linear features or prominent objects in your vicinity  Must be able to identify the same features on the map o One Linea Feature  Position yourself on a linear feature shown on the map, such as a road  Then turn the map until mapped feature lines up with the real on in front of you.  The line you see between you and the features is called sight line. nd  2 method is to assume a position that lies on a straight-line extension of the ground feature.  3 option is to take up a position to either side of the linear ground feature and then to align the feature shown on the map so that it is parallel with the ground feature. st rd  1 and 3 have problems. o Two linear features (better option than one linear feature)  3 options:  1 – more to position on either of the two linear features,  2 – move to a point which lies on a straight line extension of either feature  3 – or assume a position off to one side of both features.  Turn the map until 2 features align with those on ground  3 is the least accurate o Prominent Features  Reversal in map orientation can be avoided by using 2 features to align yourself.  Move to one feature, or to a position on a line extended through the two features.  If you are located off to the side of the features, estimate your position relative to the straightedge line between the prominent features.  Identify ground features that can be found on the map. = success! o Compass Method  Firstly, need compass, a map showing magnetic north with declination diagram.  Then do this:  Find magnetic north indicator on map  Hold map under compass, turn map until compass needle lines up with magnetic north on the map  This will orient with true north as well.  Essential to take magnetic declination because true north is a bit off.  Magnetic north isn’t always shown on maps  Commit the basic declination pattern to memory. Finding Your Ground Position  Distance Estimation o Most common technique o In which you use your distance and direction to other objects to location your position on the map. o Two useful methods: by inspection and using a compass o Inspection Method  Looking at ground features without any special aids. Find ground features you find on map with ground and estimate their distance from you  First, orient your map and select a feature on the ground that you can also identify on the map  Second, estimate the distance from your ground position to the distant feature, and convert this figure to map distance unites by using the map scale.  Mark out the computed map distance along the proper direction line and you have established your position  A further complication is that farther distances are easier to estimate than nearer distances.  As you approach vanishing point (point on horizon where parallel lines appear to converge), it becomes harder to judge distance. o Compass Method  Distance estimation using map and a magnetic compass, which indicates directions magnetically buy the alignment of a magnetic needle or floating disk to the earth’s magnetic field.  Compass method of distances estimation you plot lines that interest at your position. Advantage = don’t need to orient your map before finding your position  Azimuth – angle measured clockwise in degrees between the direction line and the reference point. (Back azimuth = add 180 if less than 180, Subtract 180 if more than 180)  Resection method o Resection method – technique for locating position that involves plotting lines that cross, or resect” at your position. o Position found using this method is called cross fix o Most accurate to use three lines. o Inspection Method  3 features on ground n’ map  Backsight – draw from the known position of a distant feature back to your position. (draw
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