Sunday, September 13, 2015

GIS - Basics

Geographic Information System is an interdisciplinary field of knowledge, comprising geography, digital cartography, computer science, mathematics, image processing, pattern recognition, digital photogrammetry and remote sensing.

GIS can be defined as a system of systems collecting, processing and analysing spatio-temporal information regarding the Earth features. It involves people preparing the data, the system (input and output devices, computing platforms and networking) and the users using the system.

Operational Information Systems (urban planner, agriculture and land management systems, etc) spatio-temporal data collected over a period of time is required to be processed. These systems DO NOT exploit the TIME CRITICALITY associated with spatial data. Processing of spatio-temporal data is done by GIS.

GIS emerged primarily due to necessities arising due to use of digital maps in civil and military applications. It has left a positive impression on varied fields such as operation planning, situation representation and terrain feature measurement. However, the primary force that led to the development of GIS as an information system was thematic cartography (composition of maps based on a particular theme, collaborative visualization of operation information and application specific map generation ).

Geographic Information Systems (GIS) is a set of digital ideas and concepts designed to provide answers to questions based on mapped data. It helps in analysing mapped data to understand distributions and explain these patterns. It can be used to make predictions of future distributions and effects.

GIS is a modern enabling technology. Its applications are used in a wide range of disciplines.

Geographic Information Systems (GIS) are tools that process spatial data into information. This information can be used to make decisions about some portion of the Earth.

GIS is difficult to define as it involves integration of several subjects. There is no absolutely agreed upon definition of a GIS. The definition of a GIS depends on the person or organisation using it.

David Rhind defines GIS as a “computer system for collecting, checking, integrating and analysing information related to the surface of the Earth.”

GIS can be though of as a series of sub-systems within a larger system. According to this definition, GIS has the following subsystems:

  1. A data input subsystem that collects and preprocesses spatial data from various sources.
  2. A data storage and retrieval subsystem that organises spatial data in a manner that allows retrieval, updating and editing.
  3. A data manipulation and analysis subsystem that performs tasks on the data, aggregates and disaggregates, estimates parameters and constraints, and performs modelling functions
  4. A reporting subsystem that displays all or part of the database in tabular, graphic or map form.

Map is the fundamental tool for analysis of spatially related data.
Analysis subsystem is the heart of the GIS.
In GIS, all data are explicitly SPATIAL.
In GIS, every feature on the Earth is considered to be either a 'POINT', 'LINE' or 'AREA'.
POINTS are said to have 'zero dimensionality'.
LINE objects are “one dimensional”.
Objects that occupy both length and width are called “AREAS”.
AREAS are a series of lines that start and end at the same location.
Adding the dimension of height to areas explains the existence of SURFACES.
Point features are discrete while surface features are continuous.
The non-spatial (aspatial) information that help in the description of features in space are called the feature's ATTRIBUTES.
The measurement framework for geographic data is called, “GEOGRAPHIC DATA MEASUREMENT”. One level of measurement is the “NOMINAL SCALE” (named). Another level of measurement is the “ORDINAL SCALE”. Comparisons can be made ONLY in the “INTERVAL LEVEL OF DATA MEASUREMENT”.

The most useful level of data measurement is “RATIO”. The ONLY level of data measurement that allows a direct comparison between two spatial variables is “RATIO”.

A primary purpose of GIS is to analyse the relationship of objects in space.
The important terms related to spatial patterns are: “PROXIMITY”, “REGULAR PATTERN”, “RANDOM PATTERN” and “DISPERSED PATTERN”.
The powerful capabilities of modern GIS include the ability to ILLUSTRATE, QUANTIFY and DESCRIBE spatial associations and thus allow examination of mechanisms that cause these associations.
GIS helps identify spatial patterns and explains pattern interactions.