GIS in Irrigation andWater Management - Practices of Irrigation and On-farm Water Management - page 429

data to get the real world coordinate system. One of the key issues for the GIS
database development is to specify a common coordinate system for the database.
11.10 Data Input
There are five types of data entry systems commonly used in GIS: keyboard entry,
coordinate geometry, manual digitizing, scanning, and the input of existing digital
files.
Keyboard entry and coordinate geometry procedure : Attributes data are
commonly input by keyboard, where spatial data are rarely entered in
this way. Coordinate geometry procedures are used to enter land record
information.
Scanning : Scanning, also termed scan digitizing, is a more automated method
for entering map data. It converts an analog data source (usually a printed
map) into a digital data set.
Digitizers : Manual digitizing is the most widely used method for entering spa-
tial data from maps. It provides a means of converting an analog spatial data
source to a digital data set with a vector structure.
11.11 GIS-Based Modeling or Spatial Modeling
Geographic information systems (GIS) are quite common and generally accepted in
surveying and mapping, cartography, urban and regional planning, land resources
assessment, and natural hazard mapping, e.g., crop loss estimation; for environmen-
tal applications such as hydrological modeling, climate change modeling, and land
management. Current trends in GIS in interrogation of vector and raster data sets
resulting a hybrid GIS make easy to accommodate database layers, specifically the
remote-sensing-based satellite images and subsequent classification of the images
for spatial modeling.
Modern techniques such as remote sensing (RS) and geographic information sys-
tems (GIS) have the capabilities of water resource management and conservation
tool. RS/GIS analysis can show where water enters a system and how it leaves
through evapotranspiration and runoff. Using this information, planners can iden-
tify areas where there is potential for development of new water resources; where
water can be reallocated from one use or one basin to another; and identify potential
areas of water scarcity before water shortages occur. The GIS technique helps in
integration of satellite and ground information to evaluate the system performance
and to diagnose the inequality in the performance to aid in improving the water
management.
Approaches for modeling under GIS could be of two types: a decision support
system based on rule formation for individual layers or integrating the layers by