SCALE IS A FUNDAMENTAL component of geographic events and processes. Climate change occurs at global scales, while human diseases such as measles occur at essentially local and regional scales. Many geographic processes also occur across multiple scales, and more important, some processes behave differently at various scales. Consequently, an explicit statement of scale is required to understand and compare these geographic processes.
One of the fundamental and frequently encountered constructions of scale is related to maps and the measurement of linear distances from them. Because maps are smaller in physical size than the areas on the earth that are mapped, each map must state the ratio or proportion between measurements on the map and on the Earth. This ratio is referred to as the map scale and is a key element for measuring accurate distances on the map.
Given that the map scale is related to the transformation process between the Earth and the flat map, scale construction is a complex task. Nevertheless, there are four basic formats for depicting the scale of a map. These formats are the representative fraction, the verbal statement, the graphic or bar scale, and the area scale.
The representative fraction (RF) is commonly stated as a ratio of two numbers separated by a colon. As an example, the representative fraction 1:10,000 means that each unit of measurement (millimeters, centimeters, feet, miles, etc.) on the map corresponds to 10,000 units of measurement (millimeters, centimeters, feet, miles, etc.) on the surface of the Earth. The unit of measurement for the numerator and denominator of the RF ratio must be identical.
Another way to depict map scale is to use a verbal statement of the relationship between linear distances on the map and the surface of the Earth. The statement “one centimeter represents 100 meters” is an example of a verbal statement of scale. The graphic or bar scale uses a subdivided line to mark off systematic distances on the map and their equivalent distances on the surface of the Earth. The map units (kilometers, meters, miles, feet, etc.) are clearly stated near the graphic scale and one end of the bar is usually further subdivided to allow more detailed measurement of distances. The area scale is a graphic depiction that provides information about how much area on the surface of the Earth is represented by a unit area on the map.
In some cases, a map scale may not be evident on the map. Fortunately, the map can still be useful. An estimate of the scale can be determined as follows: select two fixed points for which you know their separation distance in the real world, measure the map distance between these two fixed points, and then divide the map distance by the real world distance for the fixed points to obtain the representative fraction.
The selection of an appropriate map scale must give consideration of the intended purpose of the map, the target audience, and the geographic events being depicted. Geographers use the term small scale to mean that the map shows a large section of the Earth and hence only generalized surface features. On the other hand, a large scale map shows a limited amount of the Earth's surface and hence depicts a large amount of detail.
Scale also has an effect on the amount of distortion embedded in the map. These distortions come about because it requires greater effort to flatten out larger curved sections of the Earth so that they can fit on a flat map. For maps showing large sections of the Earth (small scale map) the potential for distortion is great. For maps showing a limited section of the earth (large scale map), the distortion is not as great. Thus, measuring distances on continental and global maps should be treated with caution and the results used only as an approximation.
The gradual expansion of geography into many areas of societal and environmental problem-solving has demanded greater consideration of scale beyond the dominant cartographic traditions. For example, human geographers conceptualize scale based on the human body, household, neighborhood, city, and so on. This reconceptualization is particularly useful for dealing with the dynamic nature of social systems.
On the other hand, biophysical geographers use the notion of operational scale to measure and understand the context in which geographical processes occur. Geographic information scientists use the term spatial resolution to represent the granularity of the data being assessed or analyzed. As an example, satellite image A might use a smaller pixel (“picture elements”) size, 10 m x 10 m, in comparison to another satellite image B, 100 m x 100 m, to represent a selected study area. Image A is said to have a greater spatial resolution or finer grain than image B. In recent times, the impact of the internet on integrating the local with the global has radically shifted perceptions about scale in economic and social geography. Newer definitions of scale based on networks of interconnecting objects are now dominating the scale discussions in regional economic geography studies.
The rich definitions and interpretations of scale outlined above are both a challenge and a benefit. The challenge usually occurs when it comes to understanding scale concepts across subdisciplines. This causes a mismatch in syntax and semantics with negative consequence for scale integration and understanding of processes. However, context-dependent constructions of scale provide more flexibility and critical awareness of our understanding and representation of reality.