How to Choose the Map Scale ?

On a small-scale map, such as a page-size map of Switzerland, places of religious worship occur at points, but on a large scale map, such as a map of a local neighbourhood, individual buildings would likely be apparent, and thus the focus might be on the area covered by the place of worship.
Similarly, a river could be considered a linear phenomena on a small-scale map, but on a large-scale map, the emphasis could be on the area covered by the river. So, the map scale must be adapted to:

• The map content: Some special themes can not have various scales, but only the most logical one. For example, population density maps cannot be larger than 1:100 000 otherwise the mapped people are not representative (commuters, day labourer, etc.).
• The map purpose: The map scale must be adapted to the purpose of the map and not to the first design or aesthetic idea of the author. Here you should think how wide will the earth area to be mapped be?
• The map precision: With what measuring and counting will the map be built? Here you should think how detailed the information you display on the map will be. With large scale maps, the information is precise because they are less generalised.

Large scale maps are on the whole not economic, not easy to handle, and sometimes misleading. And, small scales make on the whole the map difficult to read, complicate, and sometimes are meaningless. Which scale is selected for a given map design problem will finally depend on the map purpose and physical size. The amount of geographical detail necessary to satisfy the purpose of the map will also act as a constraint in scale selection.
Generally, the scale used will be a compromise between these two controlling factors. When you represent the scale graphically on the map, the measurement dimensions and the line thickness should be adapted to the map graphics.