Strictly speaking, Todd was never a practicing surveyor. However, his involvement with the surveying profession in South Australia was extensive. Initially, Todd was a user of surveying services. His best known accomplishment, the establishment of the Overland Telegraph, utilised a large number of surveyors, many having been trained by noted Surveyor-General George Goyder.Arguably, Todd's best known 'field survey' took place in May 1868, when he undertook astronomical observations near Chowilla to determine the position of 141st meridian, being the border between South Australia and New South Wales. The survey was a response to a growing suspicion that the border between South Australia and Victoria (which was also supposed to coincide with the 141st meridian) had been marked in the wrong position.Todd proved that the marked border between South Australia and Victoria was too far west by at least 3.6 km, sparking a legal battle between the two States. Eventually, in 1911, the High Court of Australia ruled that the surveyors' marks constituted the boundary, and the fact that it did not exactly coincide with the 141st meridian did not warrant the re-adjustment claimed by South Australia.
Examiner of Surveyors
In 1882, Todd was elected as inaugural President of the South Australian Institute of Surveyors, a position that he retained until 1888. One of the Institute’s first actions was to seek the establishment of a Board of Examiners to recommend the issue of Surveyors’ Licences to cover legal surveys. With the joint support of Todd and Surveyor-General George Goyder, the Licensed Surveyors Act was proclaimed in 1886. Candidates for Licences were examined in mathematics, survey instruments, drawing, the field practice of land surveying, and astronomy. Todd continued to set and mark the astronomy exam papers until his retirement in 1905.
One of the functions of colonial astronomers was to fix absolute positions in their newly settled lands by referencing the positions of celestial bodies using positional astronomy (astrometry). Todd’s work in this field brought him into a close relationship with the surveying profession.As the moving force behind the construction of a continental telegraph system, he relied on the practitioners of surveying to determine suitable routes for 10,000 kilometres of telegraph lines. Todd not only relied on surveyors, but he also helped establish them as a recognised profession in the Colony. He acted as inaugral President of the South Australian Institute of Surveyors and served as the examiner in astronomy, one of five topics covered by candidates for Licenses in Surveying.