Criteria for selecting a suitable scale

The scale of a map should be chosen after considering the following points:

1. Purpose of the map. Detailed engineering plans (building, road design) need a large scale such as 1:100 to 1:1000; reconnaissance or index maps use a small scale such as 1:50,000.
2. Extent of the area. A large area drawn at a large scale needs huge drawing sheets; the scale must let the area fit on a convenient sheet.
3. Accuracy and the smallest plottable length. The smallest length that can be plotted is about 0.25 mm. The ground length represented by 0.25 mm (0.25 mm $\times$ scale denominator) must not be more than the required ground accuracy. For an accuracy of 0.1 m, the scale cannot be smaller than 1:400.
4. Amount of detail to be shown. More detail needs a larger scale.
5. Size of the drawing sheet and ease of handling and storage.
6. Cost and time. A larger scale means more field work, cost and time.
7. Convenience of reading. Round RFs (1:500, 1:1000, 1:2500) make plotting and reading easy.
8. Standards of the department, e.g. the Survey Department of Nepal uses 1:500 to 1:2500 for cadastral maps and 1:25,000 for topographic maps.