13.3 Data Input and Editing

a. Role of data input and editing
Data acquisition occupies about 80 percent of the total expenditure in GIS. Therefore data input and editing are very important procedures for the use of GIS.

b. Initial data input
Geometric data as well as attribute data are input by the following methods.

(1) Direct data acquisition by land surveying or remote sensing
Vector data can be measured with digital survey equipment such as total stations or analytical photogrammetric plotters. Raster data are sometime obtained from remote sensing data.

(2) Digitization of existing maps (see Figure 13.3.1)
Existing maps can be digitized with a scanner or tablet digitizer. Raster data are obtained from a scanner while vector data are measured by a digitizer. In GIS, raster data and vector data are frequently converted to vector data and raster data respectively, which are called raster/vector conversion and vector/raster conversion respectively.

c. Editing
Editing is needed to correct, supplement and add to the initial input data through interactive communication on a graphic display using the following procedures.

(1) to input manually or interactively those complicated attributes which are not effectively digitized in the initial input stage.

(2) to correct errors of input data or to supplement with other data.

d. Problems in Data Input and Editing
There are two main problems.

(1) Manual operations
It is difficult to automate data input and editing because of unremovable noise and incomplete original maps, which result in a large amount of manual work with resultant inefficiencies in time and cost.

(2) Unreliability of input data
As the input involve many kinds of errors, mistakes and misregistration because of the manual input, further effort should be applied to obtain data high quality and reliability.


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