The graphic scale is a visual representation that allows to know what is the proportion of the lengths in a plane with respect to the real lengths. By the very fact of being graphical, these scales allow us to intuit the real distances without resorting to complicated calculations.
This modality of graphic representation originated towards the end of the 13th century in Italy. The first map in which this type of technique was observed was the navigation chart of the Mediterranean and surrounding areas, known as the Pisana Chart.
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This type of scale is used in multiple disciplines, and they have greatly facilitated the interpretations of the dimensions of reality by man. The main uses are focused on cartography, engineering and architecture.
History
There is reference to the fact that the Pisan Charter was the first time that a graphic scale was used in cartography. This map was found in the city of Pisa in the 13th century, where it takes its name. In essence, this find was intended for navigation.
It has several characteristics. The map shows the Mediterranean Sea, the Black Sea, as well as the Atlantic Ocean as a whole.
However, the chart becomes inaccurate when it comes to the Atlantic Ocean and it shows in the distortion of the British Isles. The great peculiarity of the map consists in its scale based on segments corresponding to 5, 10, 50 and 200 miles.
To achieve this scale, the map makers appealed to geometric figures. These shapes establish a proportional relationship between the measurements on the chart and the actual measurements of the earth's surface.
Portulan charts
Since ancient times there have been attempts to make navigation charts that express routes, as well as coastlines. In fact, the Pisan Chart is in line with the Portulan charts and gives a detailed description of the coastline, but without details regarding the topography.
The portulan charts follow the same spirit of the maps that arrived until the Modern Age for navigation. They also have a grid that accounts for both navigation directions and winds. Additionally, they have the so-called trunk of leagues or graphic scale.
This chart format was used by Arab, Portuguese, Majorcan and Italian sailors. Also, with regard to engineering scales, there is knowledge of the so-called scale boxes that were used in the 19th century.
Evolution of graphic scales
The representations of the graphic scales evolved from the patterns in the form of geometric figures until they reached a narrow bar. This change occurred from the fourteenth century.
This bar graphically establishes the analogy between the measurements of the map or chart and the actual measurements. The bar can be arranged both horizontally and vertically and is known as a "trunk of leagues".
In these first bars the corresponding numerical values were not placed. By then it was virtually a norm that the correspondence between distances was 50 miles for the case of Portulan maps.
In the case of marine charts, the well-known Mercator projection was used. This consists of a cylindrical projection that is made tangential to the equator of the earth. For this reason the Mercator projection has distortions depending on the latitude.
Today the same philosophy of the Portulan maps is still used. Likewise, this type of scale represents an advance with respect to lexical scales, which are subject to confusion due to disused terms.
For example, it usually occurs on lexical correspondence scales between inches and a virtually unused unit, such as the furlong. This unit is known only to people familiar with the culture of the British Empire.
What are they for?
Graphic scales are used primarily in cartography, engineering, and architecture.
In the case of cartography, we usually talk about 3 types of scales depending on the terrestrial dimensions to be represented. Thus, there were large-scale, medium-scale and small-scale maps.
The small scale refers to planes where large real extensions are represented in a very small space. These are essentially from countries or the entire globe.
On the other hand, large-scale ones are used to represent not so large tracts of land on paper. Similarly, maps of the earth can be distorted in terms of their scales. This distortion will vary according to the type of projection and is due to the spherical character of the globe.
The graphic scales used for engineering arose when greater accuracy was needed in the elaboration of mechanical parts. For this reason, the complexity of civil engineering structures from the Modern and Contemporary Ages made these scales a necessity.
Primarily, engineering scales are given in proportions ranging from 1:10 to 1:60, depending on the actual quantities to be represented.
Additionally, the appearance of the scale for uses related to engineering and architecture has been vital. This instrument is a kind of prismatic ruler and has different scales on each of its faces.
Examples
The graphic scales vary according to the type of use that they want to be given, as well as the magnitude to represent. On a graphic scale a segment could imply a real length of 50 km.
For example, we could have a trunk of leagues with a total length of 5 centimeters equivalent to 500 kilometers. Likewise, this trunk of leagues could be subdivided into 5 subsegments, so that each subsegment would actually be equivalent to 100 km.
This relationship between actual dimensions and dimensions in the drawing can vary from a large scale to a small scale. This is according to the correspondence between the magnitudes.
Graphical scales are an important tool to represent aspects of the real world at the plane level. They allow greater accuracy for navigation, as well as for construction and industry.
References
- Talbert, R., & Watson Unger, R. (2008). Cartography in Antiquity and the Middle Ages: Fresh Perspectives, New Methods. Leiden: BRILL.
- Bagrow, L. (1985). History of Cartography. New York: Routledge.
- Cattaneo, A. (2011). Fra Mauro's Mappa Mundi and Fifteenth-Century Venice. Turnhout: Brepols Publishers.
- Harvey, P. (1996). Mappa mundi: the Hereford world map. London: Hereford.
- MacEachren, A., & Taylor, D. (2013). Visualization in Modern Cartography. London: Elsevier.