History of Coordinate Systems Used in Malawi

In the old days, surveys (mostly cadastral) in the southern region of Malawi were based on the Zomba local system. This was a local triangulation scheme with two loops and a misclosure of 14 feet. Surveys outside this triangulation were based on a local origin using the star, sun or compass for orientation. 

By the year 1960 two different grid systems were being used in Malawi as in Zambia and Rhodesia. These systems include the Gauss Conformal grid system used for cadastral surveys and the Universal Transverse Mercator (UTM) grid system used for topographic mapping. This entails that each station in the triangulation had two sets of coordinates.

The Gauss Conformal grid system covered 2° belts of longitude across the country. Its origin was defined by the central meridian of each belt (longitude 33° and 35°) and latitude 0° at the equator. This system used the Transverse Mercator projection with south as its orientation. Both negative and positive coordinates were obtained and feet was the unit of measure. The longitude 35° belt (LO35) was used in southern region plus Ntcheu, Dedza and Salima districts whilst the longitude 33° belt (LO33) was used in the remaining parts of the country. 

In 1966, some distortions were discovered in the southern region and conversions from LO35 (1960) to LO35 (1966) were done. The UTM grid system had a 6° belt across the country. The longitude of origin was longitude 33° with false eastings 500 000m and the latitude of origin was the equator (0°) with false northings of 10 000 000m. The system used metres as the unit of measure, a north orientation and only positive coordinates were obtained.

The main reason for using Gauss Conformal over the UTM grid system for cadastral purposes was to minimise corrections applied to measured quantities. Thus, conversions of observed spheroid distances to projection distances and observed spheroid directions to grid bearings required larger scale factors and convergence (t-T) corrections respectively. Distortions due to projection were greater at the limits of the zones.

The UTM grid system was adopted for cadastral surveys in 1973 as it was being used widely across the world and the process of converting LO33 and LO35 coordinates to UTM grid system was simplified by electronic computers. As of today, two UTM grid systems are being used in Malawi; one is based of  Clarke 1880 modified ellipsoid and the WGS-84.