Saturday, January 31, 2009

What the fuck is GIS ?

GIS for a layman and for everyman who wants to lay !!!!


What is GIS ?

Some call it Geographic Info Systems, some call it Geographical

Information Systems, some people see it as a field of academic study

called GI Science. You even get a Master's and Doctorate in this field

of study.

Defining GIS is not a simple task. It is percieved differently by

different people. some people think it as a branch of IT, some think

it to be computer-assisted mapping systems, some as cartographic

application, a type of database systems or a ....... some of my friends

even thought of it as Girl Information System.... ;-)

I am not getting into Perception and cognitive science.....


My Cricket coach always asked me to go by the book. so I am going by

the definition in this book on "Concepts and Techniques of Geographic

Information Systems by C.P.Lo and Albert K. W. Yeung", which is

GIS is a set of computer-based systems for managing geographic data and

using these data to solve spatial problems.

As IT professionals I expect everyone of us to know what data and

information is all about. some of us even know what metadata is.

A question must arise in our minds that what is the need of yet another

Information system.

The speciality of GIS lies entirely in the data. Geographic data or

spatial data is special since it is multi-dimensional. The any other

form of data can be called as non-spatial or attribute data.

Some of our mechanical engineering friends might be thinking about the

CAD/CAM systems. GIS offers much more that a simple CAD/CAM system.

The other main interesting aspect lies in its ability to make the user

visualize spatial data in the terms of the maps they can produce, which

is the cartographic side of GIS. Which is missing in AUTOCAD.

Why does the multi-dimensionalness pose a challenge?

Some of our computer science friends must be well aware of the Balanced-Trees or the B-Trees.
These data structures are used in the context of RDBMS for the indexing or ordering of data or tuples in a table.

we all know that we can only index 1 column using 1 tree. I hope I am right here. This column is usually the Primary key.

As all the well know RDBMS are suited only for the non-spatial data.

Why cant it be used for spatial data. Since it is multi-dimensional.

As we all know we can represent a point P in 2-D space using cartesian coordinates using as (x,y).


We all are well aware of the fact that both x and y are independant of each other but the point P needs both x and y for it to be represented.

Let us take the problem of finding the nearest ATM from our office.
If we represent all the points of interest in this problem as a Points in 2-D space. It is a problem of ordering in 2-D space.

Some mathematicians might argue that is a problem of topology !!!

Hence a Spatial Analysis problem. Can we use B-Trees for this ? No ...

so we need a new kind of a data structure for this which is called an

R-Tree. Hence the databases also special and called spatial Databases.

We can order the data using R-Tree on the basis of radial distance and

find the nearest ATM.

So GIS is a about data, Information System, Cartographic System and a

Spatial Analysis tool.



Maps and GIS.

GIS as a cartographic application. GIS gives us the capability of

visualizing the spatial data and the spatial distribution of the

non-spatial data in terms of the maps they can produce. One of the most

important aspect when displaying a map is the Map Scale.

The scale of a map is the ratio or proportion between the distances

measured on the map and the corresponding distances measured on the

ground.
YOu can do the mathematics.

Classes of Maps


1) General Purpose or Reference maps: These are maps not designed for

any specific applications. This class of maps focus on locations and

shows a variety of physical and cultural features such as drainage,

roads, railways, airports, forest and cultivate areas etc. They server

as the base maps for developing and integrating other form of

geographic infomation.

2) Special Purpose or Thematic maps:

These maps are designed to depict a particular type of feature or

measurement only. Like it can show the variation of rainfall across

certain region. These maps are generated using the base maps.


2 comments:

Prasad Patil said...

Google search for "What the fuck is GIS?" gives your ranked fourth. Nice way to improve your Google search ranking. 8 in 10 are bound to search this way.

mamu said...

10 in 10 to u Mr. Prasad for observing such it...But still explanation given is really in laymen's terms...