In the earlier articles we learned about what is GIS and what are different components of GIS.
In this article, we will discuss about various techniques that are used for inputting data into GIS.
We mainly input 2 different types of data in GIS. First one is spatial data, and the second one is attribute data.
Following are different types of techniques used for inputting data into GIS.
DATA INPUT TECHNIQUES IN GIS:
This technique is also called as keyboard entry method. Data is inserted into GIS using the keyboard terminal of the computer. It is possible to enter both spatial (such as coordinates of locations etc.,) and non-spatial data using this method. However, this method is widely used for storing attribute data.
When no of entries becomes huge, this method becomes difficult to perform as fatigue and impatience of operator may affect the precision of data entry.
However, this method is most precise and accurate compared to other methods as details entered directly by the user, and no changes (from what are observed in the field or log book) are expected to reflect in the map.
This is one of the most common and widely used data input techniques in GIS. A variety of hardware is deployed in this method depending on method of digitizing. Following are 2 different types of digitizing techniques.
Heads down digitizing:
In this method equipment such as a digitizing table, a hand held tracing device (such as digitizing pen or marker), computer etc., are used in the process of digitizing. A base map is used for delineation of features.
The base map is attached to a digitizing table. Digitizing table consists of a fine wire mesh, the positions of which are controlled and calculated in GIS frame work attached to it. After, placing the map on table, it is pinned in a fixed location and georeferencing is performed.
Then the boundary and other required features from the base map are digitized by tracing along them using the digitizing pen.
This entire process is called heads down digitizing as the operator keeps his head down during entire process.
Heads up digitizing:
This is most common way of digitizing performed in laboratories and institutions. Here, a digital base map is collected and is georeferenced using GIS software. Then all features in the map are digitized using the computer mouse, while looking at the geometry of objects on computer screen.
In this process, operator keeps his head up, and hence called as heads up digitization.
Digitization results in shape files, which are vector features.
Manual digitization is a tedious job and if operator is not efficient it may lead to several digitizing errors. Hence, it has to be done with most skill and caution.
Scanning is much faster way inputting data into GIS. In this technique, scanners are used for creating a map in digital format. Scanners makes use of an electronic detector for encoding the data into GIS.
Following are different types of scanners used in this process.
- Laser scanner
- Flat bed scanner
- Rotating drum scanner
Each scanning device has its own advantages and disadvantages, which may be beyond the scope of this article.
Scanning normally results in raster data sets. However, with current advancements some scanners and GIS applications are capable of producing vector files directly from scanned inputs.
However, data cleaning or editing process may be needed for such results generated from the scanning as some discrepancies may exist in it.
Coordinate Geometry Method:
This technique is also called as COGO method. In this method survey measurements such as bearings and lengths are taken as input and entered into GIS using keyboard. Coordinates of objects and features are calculated by the GIS. This input technique produces highly accurate results and is useful in preparing cadastral maps. However, it takes lot of time, manpower and cost to produce the maps compared with normal digitizing process.
Direct File transfer:
There are many public and private sources for collecting GIS data. At present many organizations are preparing and selling GIS data sets. If any such data is available, it is possible to collect and transfer the files directly into GIS after making adjustments as per the current application.
Other than this, the satellite imagery acquired from space and digital aerial photographs are also compatible with GIS to be readily processed.
Thus the above or some of the widely used data input techniques in GIS. The selection of a particular data input technique depends on several factors such as how the data is collected, what precision is required in the out put, resources and time available, cost of project etc.
Websites and Online Resources:
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