A GIS SOLUTION TO LAND CONSOLIDATION TECHNICAL
PROBLEMS IN MOROCCO
El Hassane SEMLALI, Morocco
Key words: land consolidation, reallocation,
conceptual data model, CONGOO, database, GIS, parcel, soil classes,
precision.
Abstract
In Morocco, among important agricultural projects, land
consolidation constitutes a dynamic mean for the development of the
rural world. Unfortunately, land consolidation projects do have a
great number of administrative and technical problems.
Our objective in this study is to show the contribution of GIS to
find a solution to these technical problems. This solution concerns
especially land consolidation in irrigated areas, it is based on five
main key points:
- Establish a conceptual data model
- Conceive a prototype database
- Find a solution to computational and overlaying problems
- Examine a solution to land redistribution problems, taking into
account the constraints of the project and the landowners'
requirements
- Quantify the reallocation process, estimate the precision and
analyze the results.
Using CONGOO formalism, a conceptual data model is
established. This model illustrates both data before and after land
consolidation and their relationships. According to this formalism,
the established CDM contains 2 layers of geographical objects, 20
classes, 29 objects, 4 relationships of structure, a constraint and
near two thousands of topological relationships.
Then a database is built based on the georelational model of
ArcInfo. The spatial information identified in the conceptual level is
assigned the corresponding entities in ArcInfo representation.
Entities are classified as function of their geometric representation,
such as point, line and polygon.
After that, we suggest a methodology to solve computational,
overlying and reallocation problems, this methodology tries to find
solutions to imposed constraints such that:
- Landowners' requirements
- The reallocation according to the habitat
- The reallocation according to the soil class that occupies the
greatest area in a land ownership
- The reallocation on very neighbor soils of the situation before
land consolidation
- The reallocation closest to the old position of each land
ownership.
The outline of the proposed methodology is subdivided into three
parts:
- The first part is a computed redistribution that may be
conducted using four different methods depending on the
requirements of the farmers, the administration priorities and the
constraints imposed by the project. After analysis, the leader of
the project may choose the solution that satisfies the most
important criteria and the repartition of the redistributed soils.
- The second part is a graphical redistribution based on the
results obtained in the first part. It is an iterative procedure,
which determines the final position of the new properties taking
into account the imposed tolerances on the redistributed values.
- The third part of this methodology concerns the analysis
of the results obtained. The parameters used in this analysis are:
parcels displacements with respect to old positions, satisfied
constraints and the percentage of soil areas before and after
redistribution process. A global factor of satisfaction is used to
evaluate the performance of the achieved results for the whole
project.
The proposed methodology was conducted to three applications. The
results show that the graphical redistribution is more time consuming
than the computed redistribution, all constraints are satisfied, most
of the properties are redistributed near their old positions, most
landowners receive equivalent percentage of soil classes, and the
redistributed values do meet the allowed tolerance.
This study terminates with the estimation of the precision of
overlay operations in land consolidation projects. Results of
overlying parcels to soil classes are influenced by three main
factors: the coordinates of soil class limits, shape of parcels and
intersection angles. The precision of the attributed areas is very
influenced by that of soil class limits.
CONTACT
El Hassane Semlali
Institut Agronomique et Vétérinaire Hassan II
Filière de formation en Topographie
B.P. 6202
Rabat
MOROCCO
Tel. + 212 37 68 01 80
Fax + 212 37 77 81 35
Email: e.semlali@iav.ac.ma
24 March 2001
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