A. Sadjadi

Application of GIS in Soil Survey Projects

Soil survey projects are typically accomplished through several steps:

1 - Field study (including laboratory tests)
2 - Determination and codification of soil characteristics in each observation point as described in profile description cards.
3 - Calculation of land classification symbols.
4 - Identification of soil series and subseries and other taxonomic categories.
5 - Determination of requisite reclamations, based on existing limitations and c calculation of land irrigability.
6 - Preparation of different maps and charts.
7 - Preparation of final report.

Considerable staff time and energy is often spent to prepare numerous maps and tabular data by traditional procedures in which maps and data tables are manually processed.

Through GIS, this time-consuming and costly procedure can be accomplished in considerably less time with reduced expenditure and increased precision and analytical capabilities.

The automation of soil survey projects essentially starts after evaluation of field and laboratory data. Each profile description card is studied and soil characteristics in each observation point is evaluated and codified. A master data base is then prepared, which includes all the observation points and their corresponding data. This soil data base system is then processed by an integrated program (SDBS). This process includes steps 3, 5, and part of step 6 of the traditional procedure: land classification symbols are calculated, requisite reclamations and land irrigability is determined.

A point theme is then created in GIS environment with each point representing an observation point. This point theme is accompanied by a PAT (Point Attribute Table) which is the imported data base file containing codified soil characteristics and calculated parameters of each observation point. Spatial variations of soil characteristics can be easily shown in GIS environment through "point marking" on the basis of overall homogenity of soil characteristics. (Observation point with similar characteristics can be shown by the same color or symbol.)

A physiographic map, derived from aerial photos through stereoscopic interpretation, can be prepared and digitized to form a polygone theme. These two themes, colored point theme showing spatial variations of soils and polygon theme characterizing physiography (geomorphology) of the project area, are then superimposed and matched to delinate final soil mapping units.

Soil mapping units, forming the skeleton of the final soil data base, are then labeled and related by apprpriate GIS functions to tabular data base containing essential soil characteristics, to form an intregrated soil coverage, comprising both spatial and descriptive informations of soil mapping unit.

The resulting coverage is then analyzed using the facilities of GIS and tabular data base, numerous typical maps, i.e. soil map (soil series and subseries), land classifications maps, land irrigability maps, salinity and alkalinity maps, etc. are then derived and plotted automatically.

A Sadjadi
Mahab Ghods Consultants
Tehran, #17 Takharestan Alley
Shahid Vahid Dastgerdy Ave
Post Code: 19187
I.R. of Iran
P.O. Box 15815-1791
Telephone: 011-9821-222-0777
Fax: 2276487