Surveying and mapping ruler convenient to protect for building

The invention belongs to the technical field of building surveying and mapping rulers, and particularly relates to a building surveying and mapping ruler convenient to protect. The bottom of the ruler body is fixedly connected with a base; the side wall of the ruler body is fixedly connected with a first supporting rod; the first supporting rods are symmetrically arranged in multiple groups; the other end of the first supporting rod is slidably connected with a buffering ring. The buffer ring is arranged in a C shape; a sliding groove is formed in the middle of the buffering ring. The first supporting rod slides in the sliding groove. A first spring is mounted between the side wall of the sliding groove and the first supporting rod; the first springs are symmetrically arranged on the two sides of the first supporting rod and fixedly connected with the side walls of the sliding grooves correspondingly. In the step, the ruler body can be buffered by arranging a buffer ring and a first supporting rod when the su