Fig. 4

Examples of the features of interest identified in the Survey of India historical maps, as they appear in the different examples and editions of the SoI historical maps that cover the study area. Mound features appears as contours (A) and hachures (B) in the 1900s editions and as form-lines (C, D) in 1930s and 1940s editions. Automated detection has been applied to 1900s and 1930s editions, but not to 1940s, due to the limited number of maps. Specially in the 1930s editions, small form-line features were used to represent barren lands and small outcrops (G), which introduces false positives that needed to be filtered. Limited false positives (E–F) can be induced by the similarity of certain features. Some missing elements have been also detected in the manual inspection (H). For more details see Garcia-Molsosa et al. [22] and Table 1. Features related to the hydrographic dynamics are also represented in the historical Survey of India maps, though their aspect differs a bit in the different editions. Here we have delimited the active floodplains (I, J), disconnected channels (K, L), and dry or intermittent channels oxbows and isolated meanders (M, N)