A GIS is an information system capable of assembling, storing, manipulating, and displaying geographically referenced data. So the building of a GIS is a chain of operations that leads us from planning data observation and collection, to their storage and analysis, to the use of the derived information in some decision making process.
The main components of a GIS are:
Data is the most expensive GIS component. Digital data are collected from many sources such as aerial photographs, satellite images, field samples, and scanning or digitisation of hard copy maps. In this work several different data types were utilised to build a GIS (Table 4). In this step, software as EASI/PACE v7.0, Cartalinx v1.2, and MS Access 97 were used.
|
Thematic data |
data Type |
|
|
Field survey database |
Alphanumeric |
|
|
Soil analysis database |
Alphanumeric |
|
|
Georeferenced multitemporal Landsat images |
Raster |
|
|
Land unit map |
Vector |
|
|
Sampling points |
Vector |
|
|
Ancillary GIS layers |
geological map |
Vector |
|
road network |
||
|
drainage network |
||
|
Ancillary datasets |
field photos |
Raster |
|
climatic data |
Alphanumeric/Vector |
|
|
others |
[Various] |
|
Table 4 - Different data types
One of the main key elements of this work is the building of the database capable for the storage, retrieval, and sharing of the data in an easy and efficient way. The database consists of detailed information obtained during the field observation, describing the site and land facets of a particular land unit in terms of geomorphology, soil, and vegetation. These are entered in the database in form of relevés.
The point observations made for each land unit contain information about site location (name of the place, co-ordinates, and photo number), preliminary and final land unit code, land facets of which the land unit is composed, the relationship between land facets, and several other parameters regarding morphology, soils, and land use/land cover. The main objective of this phase is making the data ready for various types of classification for different applications mostly for land suitability evaluation. For each theme, data are selected and extracted from the data base and exported to elaboration software (spreadsheet and GIS) to produce the required output. In this step EASI/PACE v7.0, MS Access 97, MS Excel 97, and Arc View v3.1 were used.
The manipulation and analysis of data determine the information that can be utilised by the GIS. Analysis is a process for looking at geographic patterns in your data and at the relationship between features; and this can be as simple as making a map or as complex as involving models that mimic the real world by combining many data layers. Manipulation involves transformation (i.e. from raster to vector data structure), generalisation, overlay, and interpolation procedures. As original data tend to be too detailed and complex, aggregation or classification is often needed for display or communication purposes. For this part EASI/PACE v7.0, MS Access 97, MS Excel 97, Arc View v3.1, Idrisi v32.05, Cartalinx, and Surfer v5.01 were used.
The final stage is the presentation of the result to the end users and decision makers. The results of GIS can be reported as a map, values in a table, or as a chart. For the final maps and the report Arc View v3.1, ACE v3.2, Photoshop v5.0, and MS Word 97 were used.