Railway surveying and mapping scale

A ruler for railway surveying and mapping relates to the technical field of surveying and mapping rulers. A scale box used for loading a second scale is arranged on the back of the first scale, a positioning block is arranged in the middle of the end, close to an opening of the scale box, of the first scale, a positioning groove matched with the positioning block on the first scale is formed in one end of the second scale, and meanwhile a transversely-through mounting hole is formed in the end of the second scale. The second ruler is clamped on the first ruler, and the positioning block is inserted into the positioning groove. When the height of the first scale does not meet the requirement, the lock catch is rotated and the cover plate is opened, and the compression spring loses constraint and releases elastic force to push the pressing block and drive the second scale to pop out of the scale box. The second ruler is inserted into the positioning block, and bolts are sequentially inserted into the positionin