INTRODUCTION TO CARTOGRAPHY

Introduction

A map can be simply defined as a graphic representation of the real world. This representation is always an abstraction of reality. Because of the infinite nature of our Universe it is impossible to capture all of the complexity found in the real world.

For example, topographic maps abstract the three-dimensional real world at a reduced scale on a two-dimensional plane of paper.

Maps are used to display both cultural and physical features of the environment.

Standard topographic maps show a variety of information including

i.  roads,

ii. land-use classification,

iii. elevation,

iv. rivers and other water bodies,

v. political boundaries, and

vi.  the identification of houses and other types of buildings.

Some maps are created with very specific goals in mind. Figure 2a-1 displays a weather map showing the location of low and high pressure centers and fronts over most of North America. The intended purpose of this map is considerably more specialized than a topographic map.

 

Figure 2a-1   

The following specialized weather map displays the surface location of pressure centers and fronts for Saturday, November 27, 1999 over a portion of North America. The art of map construction is called cartography. People who work in this field of knowledge are called cartographers. The construction and use of maps has a long history. Some academics believe that the earliest maps date back to the fifth or sixth century BC.  Even in these early maps, the main goal of this tool was to communicate information.

Early maps were quite subjective in their presentation of spatial information. Maps became more objective with the dawn of Western science. The application of scientific method into cartography made maps more ordered and accurate.

Today, the art of map making is quite a sophisticated science employing methods from

                          i.             cartography,

                        ii.            engineering,

                      iii.            computer science,

                      iv.            mathematics, and

                        v.            psychology

Cartographers classify maps into two broad categories:

                          i.            reference maps and

                        ii.            thematic maps.

   Reference maps

Normally show natural and human-made objects from the geographical environment with an emphasis on location. Examples of general reference maps include maps found in atlases and topographic maps.

    Thematic maps

Thematic map are used to display the geographical distribution of one phenomenon or the spatial associations that occur between a number of phenomena

   Map Scale

Maps are rarely drawn at the same scale as the real world. Most maps are made at a scale that is much smaller than the area of the actual surface being depicted. The amount of reduction that has taken place is normally identified somewhere on the map. This measurement is commonly referred to as the map scale. Conceptually, we can think of map scale as the ratio between the distance between any two points on the map compared to the actual ground distance represented. This concept can also be expressed mathematically as: 

 

On most maps, the map scale is represented by a simple fraction or ratio. This type of description of a map's scale is called a representative fraction. For example, a map where one unit (centimeter, meter, inch, kilometer, etc.) on the illustration represents 1,000,000 of these same units on the actual surface of the Earth would have a representative fraction of 1/1,000,000 (fraction) or 1:1,000,000 (ratio). Of these mathematical representations of scale, the ratio form is most commonly found on maps.

Scale can also be described on a map by a verbal statement. For example, 1:1,000,000 could be verbally described as

 "1 centimeter on the map equals 10 kilometers on the Earth's surface" or "1 inch represents approximately 16 miles. Most maps also use graphic scale to describe the distance relationships between the map and the real world. In a graphic scale, an illustration is used to depict distances on the map in common units of measurement (Figure 2a-9). Graphic scales are quite useful because they can be used to measure distances on a map quickly.

 

Figure 2a-9:

The following graphic scale was drawn for map with a scale of 1:250,000. In the illustration distances in miles and kilometers are graphically shown. Maps are often described, in a relative sense, as being either small scale or large scale. Figure 2a-10 helps to explain this concept. In Figure 2a-10, we have maps representing an area of the world at scales of 1:100,000, 1:50,000, and 1:25,000. Of this group, the map drawn at 1:100,000 has the smallest scale relative to the other two maps. The map with the largest scale is map C which is drawn at a scale of 1:25,000.

 

Figure 2a-10: The following three illustrations describe the relationship between map scale and the size of the ground area shown at three different map scales. The map on the far left has the smallest scale, while the map on the far right has the largest scale. Note what happens to the amount of area represented on the maps when the scale is changed. A doubling of the scale (1:100,000 to 1:50,000 and 1:50,000 to 1:25,000) causes the area shown on the map to be reduced to 25% or one-quarter).