Improvement of area accuracy in general boundary areas in Kenya:

Case study of Juja – Kiambu County

Abstract

Land ownership in the vast Kenyan Trust land is through the process of Land adjudication. The Preliminary Index Diagrams (PIDs) are the official map documents that together with adjudication records constitute the adjudication register that forms the basis for determination and registration of interests and rights over land. The PIDs are produced from enlarged, marked and un-rectified aerial photographs; as a result they contain distortions to parcel area which more than often is a source of land disputes, especially in resolving the gap between area contained in the title deeds and the actual parcel area on the ground. Generally, the uncertainty in PID area is about 20% of the actual area. We propose a procedure that can be used to reduce large errors in PIDs by comparing ground survey and PID areas in Juja. To achieve the objectives of this study, PIDs of 31 large plots in Juja were prepared from un-rectified aerial photographs. The area of each parcel was measured in the usual way, using plannimeter. Ground surveyed areas for the same parcels within the area of study were obtained from existing survey plans, normally referred to as folio references (F/Rs), and also through ground survey on parcels without F/Rs. The root mean square of the differences between PIDs and ground survey (F/Rs) areas was ±14.63 hectares. The distortions increased with increase in areal size. A conversion equation was developed to reduce areal errors. Using the conversion equation on PID areas, the root mean square of the differences reduced from ±14.63 to ±2.95 hectares, representing an improvement of 80%. The correction equation obtained can be used to obtain corrected parcel areas to facilitate accurate valuation of land parcels in the PID areas. This technique is simple because it requires only PID areas and it works well.