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Note: All the posts are based on practical approach avoiding lengthy theory. All have been tested on some development servers. Please don’t test any post on production servers until you are sure.

Sunday, March 03, 2013

A Quick Intro to GIS - Part I

What is GIS
GIS stands for geographic information system. It is an integrated system used to display, store, manage and analyze data about objects on earth. It is used to perform a variety of functions on geographic information.

The system has several integrated components:
  • A graphic program used to draw maps
  • A database that links features and attributes
  • Tools to analyze, edit and manage geographic data
Why GIS - Geographic Approach
There are many challenges that our wold faces e.g; Climate change, political conflicts, limited resources, over population and pollution etc. To combat these challenges we need understanding, knowledge and integrated approaches.
By combing the science of geography with the technology of GIS, we can
  • Collect and organize data to better understand the earth 
  • analyze data to create geogrphic knowledge. 
  • Apply geographic knowledge to find solution.
this is called geographic approach.

Remember : a geographical approach is a way to gain understanding and solve problems.
GIS Information
A GIS stores two types of geographic information: features and attributes.
Features represent natural objects found on earth, such as continents, rivers and oceans.
Feaures also represent human-define objects such as counties and parcels.
Attributes describe the features in a GIS e.g; attributes of world countries might include Name, population area etc.

The functions of GIS are
  • Visutalization
  • Geodata managment
  • Geographic analysis.
People use the information from GIS to make decisions and solve the problems.
The data stored in GIS is geographically located. This means that a GIS can show you the pictures of data in form of map. Thus a GIS map is a window into your data.
For example you want to compare the population of the countries , you could look at a list of populations number in a table or you could look at a map.
The map allows you to discover patterns and relationships you cannot easily see in a table.
Types of Map
A paper map is static showing unchanging view.
A digital map is viewed on computer and may be static like a photograph.
A GIS map is more than a map. It has a database behind making it dynamic. By using GIS maps, you can do the things like
  •  Bring data in
  •  Display data in different ways
  •  Look at sets of data together to see the patterns and relationships
  •  Analyze data to create new information
GIS Map elements
A feature represents a real world object on a map. Each building, road, tree.
A feature has four components.
  •  Shape (Can be point, line or polygon, city (Lahore)  can be represented as point, river (Ravi) can be represented as a line,  country (Pakistan) can be represented as polygon )
  •  Location (can be expressed with latitude and longitude )
  •  Symbol (shape, color, outline, pattern of all of these)
  •  Attributes (information that describes the feature eg; Country attributes: Name,population, Capital etc)

A layer is a collection of features. Features in a layer represent the same themes, like mountain peaks, roads or lakes. Features in a layer have the same shape and the same set of attributes.
The ability to organize information about real world features into layers and view layers together on a map makes GIS a powerful tool for visualizing our world and gaining geographic knowledge.

Scale is the relationship between the size of the feature on a map and its actual size in the real world. Because no map can show features at their actual size, scale is used to represent the amount of reduction between map and the real world object. It can be expressed as a ratio, such as 1:24000.
This scale means that a feature on a map is 24000 times smaller than its corresponding feature in real world.
Scale can be expressed as an equivalence such as 1inch = 5miles.
This type scale is useful for measuring distances and feature sizes on a map.
On GIS map scale is dynamic (zoom in/out).

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