Scale in surveying is a ratio between a distance on the map or drawing to the distance on the surveyed ground.
It has no measuring unit because any ratio never has any measuring unit.
Why we need a Surveying Scale
While preparing a drawing from the survey data, it is clear that a surveyed object to be drawn on the paper sheet is so large that it will not possible to prepare a full-size drawing of it. The drawing (map or plan) should be reduced on a specific ratio (Scale), If you would not use the scale in this size reduction procedure of your drawing You will get a drawing as a result of this instead of a survey drawing.
It means, it is not possible for you to prepare even a single drawing (map or plan) without surveying scale.
A scale factor is a value used to increase or reduce a local (geodetic) distance so that it equals the grid distance.
In a scale, the number which is minimizing or maximizing the drawing or objects is called the scale factor.
For example, if the scale is 1:1000. Then the scale factor would be 1000 because this number is affecting the size of the map or drawing.
Scale factor usage while surveying with total station
When we conduct a survey using a total station, and we have control points established by GPS. Then we often face a problem that our control points are not matching to each other as we take observation while setting the instrument. It seems like control points are not appropriately established with high accuracy. But there involves a scale factor.
GPS consists of the curvature of the earth, whereas the total station does not. So if you put a minor scale factor, it will work with you. Often it is used 0.9996 where it is recommended to consult with GPS provider because they are creating transformation for every area to be surveyed.
Scale factor for survey drawings using Auto CAD
When you are exporting data to Auto CAD, you must include scale factor column in your point file format that is used for transporting points.
You must use the scale factor column name to define a point file format column having a calculated convergence angel. The scale factor can be described as the value to reduce or increase a local (geodetic) distance, so that is will be equal the grid distance.
It would help if you used this column when you are exporting point data. If you want to export the points using a format contain a scale factor, you should set zone in the file format and drawing in Auto CAD and turn on transformation settings for the drawing.
In Auto CAD there a command named “scale”, it is used to increase or reduce the size of geometric figures or whole drawings like a plan. After taking the command, you have to way to complete your action.
In the first way, you can put the scale factor in the command bar, and your selected figure or drawing would be scaled to you given scale factor. In the other way, you select a reference object to scale your desired plan or drawing.
If the survey drawing is represented graphically on a small scale, it is called a map..
If the survey drawing graphically represented on a large scale it is termed as a plan.
Representation of scale in surveying
There are two types of surveying scale according to representation. See the details below.
1. Numerical scales
2. Graphical scales
This type of scale is indicated in the form of numbers like 1:1000 and 1cm: 50m. It can be divided into two types. See both types below.
A. Engineer’s Scale
In this method of representing the scale is represented as a statement. For example 1 cm: 10 cm, it is indicating 1 cm on the map is equal to the 10 meters on the ground.
B. Fraction scale
One unit of the length on the drawing (map or plan) represents some number of the same unit of length on the surveyed ground, such as 1:500 or 1/500, 1:10000 or 1:10000, etc. it is known as the fraction scale. The ratio of drawing (map or plan) distance to the corresponding ground distance is known as the representative fraction. You can easily find the representative fraction for an engineer’s scale. For example, if the scale is 1= 100m, then
A graphical scale is a reference line drawn on the survey drawing so that its map distance corresponds to the convenient units of the length to the surveyed ground.
The graphical scale has the advantage over the numerical scales (Engineer’s scale and fraction scale) that you can determine distances on the map by actual scaling even the map has shrunk due to unknown reasons.