The current geodetic reference system in Kenya

The Department of Surveys is the official agency of the government of Kenya on all matters affecting land surveys and mapping. Its’ main functions are:-

• To provide and maintain plans for property boundaries in support of the Land Registration throughout the country.
• To provide all kinds of topographical and thematic maps in both rural and urban areas of the country for use by other Government Departments and the general public.

The department has been in existence since 1903.   
The current geodetic network in Kenya was established during the colonial times by the British. Since 1892, several major triangulation networks have been observed and computed by various organisations for specific purposes. Each organisation thus chose the coordinate system that appeared suitable resulting in a number of different systems. For each sizeable network, the readily available datum was used resulting in many datums for both planimetric and height control.
Doppler observations were carried out by the survey of Kenya between 1972 and 1973. The aim of the exercise was to:

• Evaluate the accuracy of the primary controls in Kenya;
• Provide geodetic control in remote and un-surveyed areas in the country;
• Strengthen the triangulation with precise position at optimum spacing;
• Contribute to the development of a single well fitting datum for the African continent.

The ITT 5500 equipment was used. Doppler positioning using precise ephemeris fixed fifteen stations distributed over the country.
The current geodetic network in Kenya is based on the 1960 Arc Datum. The coordinates are in UTM. There the two main reference ellipsoids used in Kenya are Clarke 1858 and Clarke 1880.
The datum for all heights in Kenya is the mean sea level referred to a tide gauge at Kilindini harbour in Mombasa. This gauge has however been submerged and a new one constructed and connected to some fundamental bench marks. By the year 2000, 3570km had been precisely levelled, the last 70km having been carried out by the Kenya Institute of Surveying and Mapping between 1992 to 1993.
There are three coordinates systems that have been used in Kenya:

• The Cassini-Soldner coordinate system;
• The east African war system; and
• The UTM coordinate system.

Before 1950, nearly all triangulation networks were based on the Cassini-Soldner coordinate system; hence the cadastral surveys in Kenya were also based on this system.
The east African war system of coordinates was introduced as a military system for east Africa. Its main aim was to unify the coordinate system for the British Commonwealth territories in the south, east and central Africa to avoid discontinuity in topographical mapping and grid references across territorial boundaries. The coordinates in this system have since been converted to UTM system.
The UTM system was introduced in Kenya in 1950 by the directorate of overseas survey (D.O.S), when it began providing survey work in Kenya. The system used Clarke 1880 spheroid; the unit of measurement was the international metre. The survey of Kenya has made an effort to convert all points to this coordinate system.
Problems experienced with the current geodetic network
Some of the problems that have been experienced through the continued use of the current geodetic network include:

• The existence of different coordinate systems has caused the need for regular coordinate conversion especially from Cassini to UTM system of coordinates;
• Pillars located at hills have been difficult to access and many have been destroyed; the network is also low;
• Lack of suitable points to base the transformation especially from Cassini to UTM;
• Lack of information or data from previous work as the records of surveys carried before 1950 are not readily available;
• Height data has been found not consistent having been derived from different datums;
• Equipment used earlier had lower level of precision and the network is generally weak;
• Hydrographical charts are not fully developed due to lack of controls near the Indian ocean, and around the lakes;
• Points established by space techniques are relatively few;
• Re-establishment of destroyed pillars has not been carried out fully due to high cost of classical triangulation method.

Minimizing the current problems of geodetic network
There is continued effort to solve the problems resulting from the current geodetic network. This has primarily been done using the Global Positioning Service (GPS).
Since August, 1996, Kenya Institute of Surveying and Mapping (KISM), under the mini-project has been carrying out GPS surveys on first order triangulation pillars in an attempt to establish transformation parameters between the WGS 84 ellipsoid and Clarke reference ellipsoid used in East Africa. The work is still ongoing but is experiencing problems due to lack of funds.
The Survey of Kenya is in the process of establishing continuous GPS observation stations in Kenya. The following table indicates the ongoing phase one construction of the continuous GPS observation stations:

FID	SHAPE	NAME OF COS LOCATION	SOC	REMARKS
1.	Point	LOKITAUNG	KEN
2.	Point	MOYALE	KEN
3.	Point	LODWAR	KEN	COMPLETED
4.	Point	MARSARBIT	KEN	STARTS IN 2 WEEKS
5.	Point	MERU	KEN	COMPLETED
6.	Point	MANDERA	KEN
7.	Point	WAJIR	KEN
8.	Point	GARISSA	KEN	COMPLETED
9.	Point	BONDO	KEN	COMPLETED
10.	Point	LIBOI	KEN
11.	Point	HABASWENI	KEN
12.	Point	LOKICHOGIO	KEN
13.	Point	SABAREI	KEN
14.	Point	RCMRD	KEN	COMPLETED
15.	Point	MALINDI	KEN
16.	Point	KANZIKU	KEN
17.	Point	EL WAK	KEN
18.	Point	MARALAL	KEN	STARTS IN 2 WEEKS
19.	Point	KAPENGURIA	KEN
20.	Point	KILGORIS	KEN
21.	Point	KAJIADO	KEN
22.	Point	WUNDANYI	KEN	COMPLETED
23.	Point	KWALE	KEN	COMPLETED
24.	Point	MALINDI	KEN	COMPLETED
25.	Point	ERDAMA RAVINE	KEN	COMPLETED

Level 1 or Phase 1 comprises of 25 stations of zero order accuracy with nine stations completed.
Level 2 or phase two comprise of 72 stations, first order accuracy, to be done later.
Level 3 or phase 3 comprise of 125 stations, 2^nd order accuracy, to be done later
Others include 3^rd and 4^th order types of which they are numerous in number although most of the points in this category are distributed mostly in urban areas with minimal or random distribution in the rural areas.
The locations of some Stations were changed as shown in the table below.

No.	ORIGINAL LOCATION	NEW LOCATION
1.	SHIMONI	KWALE
2.	VOI	WUNDANYI
3.	ASEMBO	BONDO
4.	PARSELOI	MARALAL
5.	KAPENGURIA	KANYARKWAT

                                       
Dimensions
Base plate is 2.5mx2.5m at 1.0 m deep
Column is 0.6mx0.6m at 2.7m deep on the ground.
Existence of IGS stations
There are two continuous GPS observation stations connected to the IGS (International Geodynamic GPS Services) stations; one is in Malindi and the other in KISM (Kenya institute of Surveying and Mapping). The station at KISM is currently not working. The data from these continuous recording stations are used for the computations of the baselines and eventual coordination of all other points.
 Conclusion
The problems exhibited by the current geodetic network in Kenya can be solved through the integration of GIS and GPS in all mapping aspects of the country. There is need for political will and financing of the Survey of Kenya in its efforts to carry out GPS observation stations through out the country. There is also the need for the government to source from the British, the early records of their geodetic surveys carried out in Kenya during the colonial times; this will greatly enhance the efforts of Survey of Kenya in trying to update the current geodetic network. The continuous IGS observation station at KISM needs to be restored to full functionality to complement the one operating in Malindi.