Before
we start:
Hello every body, we are here to
co-operate in order to build unique GIS infrastructures in our beloved country
(
I do believe that theories must come first and
applications should follow. For this reason I tried my best to introduce the
fundamental concepts in a straightforward manner and a simple fashioned-dress
that can be understood by the average reader. Experts must be patient to go
through this work, and I will be very pleased to have their comments on this work , via my email eltayeb21@yahoo.com.
Once again we are here to learn and any
comments will be very valuable to me. And “arogdoo afia” , for non Sudanese “ stay well” .
GIS Data collection:
Introduction:
In any project; data collection comprises one of the most
tedious and boring processes that any worker/researcher may face. GIS is not an
exception, experts estimated its costs to range from 50-80 % of the total GIS
project.
What is it?
GIS data collection is the process of adding up geographic
data to the database. There are so many terms valid for the GIS data
collection, like, digitizing, transfer, conversion, capture and others. In
spite of the delicate differences between those terms they all have the same
meaning “the process of adding up geographic data to the database”.
The dichotomy of data
capture:
Conventionally GIS data can be obtained in two formats,
analog or digital. The digital format can be entered directly into the
database, while the analog counterpart must be digitized first before entered
to the database. It is impossible to bring paper maps (analog map) into the
database before scanning (digitizing) and saving it in a readable file format
that can easily be brought to your computer.
Raster VS vector
datasets:
I am not here to go in detail about all the terms, but I
would like to speak in general as these papers involve average readers.
Commonly raster datasets are those datasets in which the
whole file is segmented to picture elements (pixels). Those types are
conventionally obtained via satellites imagery and aerial photographs. On the
other side stands the vector datasets, those types of data composed of features
or entities (points, lines and polygons). Classical surveying methods are used
to capture such types of data, recently modern GPS
methods were used in this process. Without going in details and debates, vector
data sets are reliable in describing features with sharp boundaries (roads,
parcels, hydrants, nodes, etc…), while raster datasets are reliable in
describing continuous fields( soil types, elevations, slopes , pollutants,
etc….)
In general GIS data can be obtained via direct data
capture “direct entry of the geographic data” or via transform entry “indirect
entry”, like transforming via different intermediate sources like ,magnetic
tapes ,CDs, internet, diskettes and etc…
Whatever the type of the data obtained, GIS data can be
sorted into two main sources;
Primary data:
These are types of data that are primarily collected for a
specific GIS project.
Secondary:
In which the data is collected for other purpose, but
transformed to fit certain GIS applications.
To be continued………