Alexander Simms worked as a human computer at the Royal Observatory, Cape of Good Hope, where he received training in surveying. He passed the examination for the certificate of proficiency in the theory of land surveying of the University of the Cape of Good Hope in 1891 and was admitted as a land surveyor in the Cape Colony in 1892. Thereafter he appears to have gone into private practice. In 1897 he was contracted to conduct a geodetic survey in Southern Rhodesia (now Zimbabwe) under the direction of David Gill*, director of the Royal Observatory, Cape of Good Hope. The object of the survey was to establish a basis for subsequent more detailed surveys and mapping of the territory, while it would also form part of the 30º East arc of meridian survey which Gill envisaged stretching north from the Eastern Cape right through Africa into Europe. Gill planned Simms's survey so that it would, among others, connect the two most important centres in the country at the time, Bulawayo and Gwelo (now Gweru). At the insistence of the British imperialist Cecil J. Rhodes the chain to be measured by Simms stretched from Bulawayo northwards, leaving the southern part of the country to be dealt with later.
Field parties reconnoitred and beaconed points to be included in the survey in 1897, while latitude, longitude and azimuth were measured at Bulawayo in 1898. Two baselines were measured, one at Inseza near Bulawayo and the other, in 1900, at Gwibi, near present Harare. These measurements were made with the Jäderin method, involving the use of two wires (of brass and iron) with different coefficients of thermal expansion. Angular measurements were made with a 10-inch Repsold theodolite and repeated eight times at each station. The heights above sea level of the stations were based on the height of a railway benchmark at Bulawayo, which was connected to sea level at Port Elizabeth. Astronomical determinations of latitude were made at fifteen stations and azimuth at four stations. The astronomical observations at Harare were completed in September 1901, when longitude was determined through an exchange of time signals with the Royal Observatory in Cape Town by means of the telegraph line. As a result of a variety of problems the field work proceeded slowly. There was a shortage of funds, oxen for transport were not always provided, Simms's first assistant and others fell ill, the theodolite was lost, and observations of angles could only be carried out between April and July because of rain and bush fires during the rest of the year. Simms's party was disbanded late in 1901 as a result of the Anglo-Boer War (1899-1902), having measured a chain with a length of about 4º, comprising 65 geodetic stations, from Bulawayo to just south of the Zambezi River. The results of the survey were published by Gill as "Report on the geodetic survey of part of Southern Rhodesia, executed by Mr Alexander Simms..." in Volume 3 of the Geodetic Survey of South Africa (Cape Town, 1905). Simms's survey was continued northwards by Dr T. Rubin* in 1903.
From 1903 to 1906 Simms was employed on the principal triangulation of the Orange River Colony (now the Free State) and Transvaal Colony, under Colonel W.G. Morris*. This work was planned by Gill to extend both the geodetic surveys of the Cape Colony and Natal, as well as the arc of meridian. Simms and W.B. Robinson* measured five baselines, at Belfast, Ottoshoop, Wepener, Kroonstad and Houts River, again using the Jäderin method. When this work was completed in July 1904 Simms and Captain H.W. Gordon* surveyed a chain from Newcastle through Belfast to the Limpopo River (656 km) as part of the arc of the 30th meridian. Simms also surveyed a chain from Pretoria southwards along the 28th meridian through Kroonstad and Lesotho to Cala in the Transkei (704 km). He completed his field work in January 1906. By that time he had become an early member of the Institute of Land Surveyors of the Transvaal.