Understanding Scale Bars


To understand what exactly a scale bar is and how it aides in drawing and map representation, we must firstly understand what scale is itself .

Covered in detail here; scale is the method of representing a subject at a different proportion to its real world size, although most commonly used as a device to reduce proportions, it can also be used to increase them.

Typically used to represent large objects and areas, such as plans of buildings and maps, scale reduces sizes down to a manageable proportion that can both be viewed comfortably as a whole, and be easily transportable via traditional paper sizes and methods.

…a scale bar is a tool that aides us with the reading of this scale when a scale rule is not available, and/or the drawing or map is not printed to its intended and specified sizing.


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What is a scale bar?

A scale bar is a linear graphic that is divided into equal segments and used to measure distances on drawings and/or maps that are produced to a set scale, but not necessarily printed to one.

Particularly within the design, architectural, and engineering professions, in many instances drawings are printed to an exact size and can therefore be measured via a scale rule. The addition of a scale bar however means that the drawing can be measured using a traditional ruler and/or via any other well proportioned object such as a credit card or posit.

As for maps, these come in a variety of shapes and sizes that due to the large areas being shown, rarely represent a traditional drawing scale, and a scale bar is therefore the only way to accurately measure distance.

Why are they important?

Aside from making map and drawing reading easier, when a scale bar is present, the drawing or map doesn’t necessarily need to be printed to a specific size. This is because the scale bar, no matter how big or small the drawing becomes, maintains its proportion to the drawings subject.

This is particularly useful when measuring via a digital screen or mobile device, and when a plotter is not available to print the required paper size.


Scale bars are bespoke to the scale of the drawing or map they are assigned to, and can only be transferred between one drawing to another if both drawings are of the same ratio (scale).

For example a scale bar showing an imperial 1:8” scale, can only be used to measure a 1:8” drawing. If the drawing is of a different scale, it requires a different scale bar to match.

For this reason and in terms of the units used as measurement, there are many variations.

Graphically however, there tends to be a few key and standard methods of representation as shown below, however equally there can be a high level of creativity in the way that the measuring segments and units are shown.

The one KEY and fixed factor is that they must be straight!.


How are they calculated?

A scale bar if often calculated at the time of when the drawing or map is complete, and before it is plotted (printed) to a set size. If for example the drawing is being plotted to a metric 1:100 scale, and the scale bar units are in meters, then each one of its segments will represent 1 meter and be 100 times smaller than the 1 meter real-world measurement.

Equally, scale bars can be drawn at a 1:1 scale, and using the relative units of measurement to match the drawing, simply be plotted to the required size to match the drawing.

How are they created?

Scale bars can be drawn in any imperial or metric unit, however this is most commonly influenced by the size of the subject needing to be scaled.

For example, a floor plan of a house would most commonly be measured in millimetres or inches, but a map that represents a much larger area would be measured in meters/feet or miles/kilometres, and the accompanying scale bars would match this.

How are they used?

A scale bar is essentially a measuring aid and device, and whilst it can be used independently, it is typically paired with a standard rule.

The rule is used to take measurements from the drawing and/or map, and then measured against the bar using the recorded distance.


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