Geography 140
Introduction to Physical Geography

Lecture: Maps (Introduction)

  I. A map is a symbolized representation of all or part of the earth's (or, 
     indeed, any celestial object's or space's) surface on a flat sheet.
     A. Uses
        1. Allows us to get a sense of relative location, of spatial 
           relationships, on a scale that goes way beyond our perspective here 
           in one little place on Earth.  This sense, of course, is of great 
           importance to all kinds of geographers and many people in many 
           other disciplines and walks of life (just try to get around in L.A. 
           without a "Tommy Guide").
        2. Additionally, they can convey all kinds of information beyond that 
           of mere location, if the mapmaker chooses data and symbolism 
           properly.
        3. A map, being flat (and possibly foldable) is much more portable and 
           convenient than a globe!
     B. The science concerned with map design, construction, reproduction, and 
        publication is called "cartography."  Mapmakers are called 
        "cartographers."
     C. The purpose of this section of the lecture is to help you understand 
        better how to read different kinds of maps and to sensitize you to 
        some of their limitations.

 II. The essential and biggest limitation of any map is the physical 
     impossibility of transferring a curved surface, like the earth's, onto a 
     flat one without distortion and error.  I cannot emphasize this enough:  
     There is simply no such thing as a perfect map.  We are stuck with this 
     limitation, though, because maps are so useful in spite of their inherent 
     defects.  Since we can't eliminate these defects, the best we can do is 
     understand them and control them for the purposes of a given map's 
     planned use.  This is the task of "projection," of how we transfer a 
     spheroidal surface onto a flat one.
     A. Properties of a map.  Ideally, a map would possess a number of 
        important properties.  Unhappily, no one map can retain all of them 
        (or we'd have a perfect map, which is an impossibility).  It is the 
        task of a cartographers to figure out which of these are most 
        important to retain for a given purpose and then project the round 
        earth onto the flat map in such a way that the key properties are 
        retained (at the expense of less important properties).  Here are 
        those properties that you, as a cartographer, try to pick and choose 
        among for emphasis in a given map:
        1. True direction.  Map directions of N-S-E-W and every direction in 
           between could duplicate those in the real world.  If N points to 
           the top of the map (which is a cultural convention), then W is at 
           right angles, 90° to the left.  Actually, only the Mercator 
           projection (more on that later) shows true direction in the sense 
           of true headings.  Other maps are "true direction" in the sense 
           that a straight line on them is a great circle route, the direction 
           of the shortest distance between two places.  This quality is what 
           is meant most of the time when a map is said to preserve "true 
           direction."  Oh, and the Mercator projection is not a "true 
           direction" map in this sense of the words, because a constant 
           compass heading will not take you on the shortest path to your 
           destination (great circle route).  Confused?  The lecture on 
           projections will organize your confusion. I hope.
        2. Equidistant (true distance or scale):  This means that, since a map 
           is a miniaturized representation of the earth, it would be nice if 
           all places on the map were reduced in the exact same amount as all 
           other places on the map.  This is, sadly, not possible, as 
           projection of a sphere onto a flat surface means some areas are 
           shown at larger scales than average and some at smaller scales.  
           Scale can be true in certain directions, though.
        3. True shape or conformality.  The shape of a landmass is shown 
           accurately, but at the cost of accurate representation of area.
        4. Equivalence of area.  If area is accurately shown, shape is thrown 
           off.  Conformality and true area are mutually exclusive virtues.  
           If you have one, you can't have the other:

           

           A and B are conformal:  They show the same shape.  A and C are true 
           area, but certainly NOT conformal in shape.  Equivalence of area 
           might not be important to a navigator, but it is very important for 
           a lot of classroom and media uses to show various distributions.

On to the next lecture, on map projections.

This next lecture looks like a lot of material, but don't faint:  Most of it 
is pictures, and I've included a study guide at the end of it.
Geography 140 Introduction to Physical Geography

Lecture: Maps (Introduction)

Geography 140
Introduction to Physical Geography
