GIS Basics



What is GIS? 


Before we get into the definition of “What is GIS?”, it is important to understand the term Geography.


Geography is a study that tries to understand the world through human and physical features, and understanding the relationship of place and location.  Geography is not just the study of where things are and how they got there but it looks at the connection between people, places, and the earth. 


Almost everything in the real world around you has a spatial component:



Here is an aerial photograph of Beaver Stadium in the real world.  We know that Beaver Stadium is located in State College and is the home field of Penn State University’s football team.  We also know that the campus buildings surround this area. 



Definition of a GIS:


A Geographic Information System is a system of computer software, hardware and data, and the personnel that makes it possible to enter, manipulate, analyze, and present information that is tied to a location on the earth’s surface.



Components of a GIS are the combination of:




                                            +                                               +




Computer Hardware

and Software


Spatial Data from

the “Real World”


Trained Personnel








Hardware is the computer on which GIS operates.  The software runs on a wide range of hardware types, from centralized computer servers to desktop computers used in stand-alone or networked configurations.


GIS software provides functions and tools needed to input and store geographic information.  It also provides query tools, performs analysis, and displays geographic information in the form of maps or reports. 


All GIS software packages rely on an underlying database management system (DBMS) for storage and management of the geographic and attribute data.  The GIS communicates with the DBMS to perform queries specified by the user.




Data is one of the most important and expensive components of a GIS.  Geographic data and related tabular data can be collected, purchased from a commercial data provider, or downloaded for free from a number of sources.  PASDA, which is the official spatial data clearinghouse of Pennsylvania, provides GIS data free of charge.


There are two types of data used in GIS:



We will explain these in further detail later in the basics.


Trained Personnel


The people who are trained to manage the system and develop plans for applying real-world problems are what make a GIS so powerful.  There is a wide range of users from a technician an analyst who use GIS to for their everyday work, or a specialist who may design and maintain a system.


How a GIS Works


In the past analyzing spatial data was a very expensive process.  Huge databases and expensive hardware and software made it difficult for everyone to use, apart from GIS experts.  Over the past few decades computers have become faster, more robust and more affordable.   With desktop computers, affordable and easy to use software, GIS can be used by anyone.


You do not need to be a “GIS Specialist” in order to learn GIS.  It is a tool like any other computer software, such as a word-processor, that allows the user to complete a task efficiently and effectively.  The user is the key to a successful GIS and the possibilities are endless.



Databases can be large and complex.  This database contains United States Population statistics.





When the data is interpreted using a GIS it is much easier to see the population throughout the US. 



It is not just the visualization of a database that makes a GIS so powerful but the combination of layering datasets and asking complex questions.  We will show an example later.


One-way to understand how a GIS works, is to look at the world as a collection of thematic layers that can be linked together by geography.  Thematic layers could be roads, rivers or buildings to name a few.  Once the thematic layers have been created with a GIS, we can begin to answer complex questions, and solve real world problems.



There are two types of geographic data models:


Raster: Grid



Below is a raster example of the National Land Cover Data Set.  This example is acquired by the Multi-resolution land characterization (MRLC) consortium.


Developed from LandSat Thematic Mapper Satellite Imagery and produced as a cooperative project between the USGS and the US EPA

National Land Cover Dataset


Raster data is a structure composed of rows, and columns.  Group of cells with the same values are used to represent features. This example below is zoomed in to the Harrisburg area. 




In this example, dark red is used to represent High Development, as in the case of Harrisburg, Camp Hill, and Mechanicsburg.  These cells have a value of 3.  Blue is used to represent water.   Cells that define the Susquehanna River have a value of 1.








Vector: Line



This is an example of Centre County (polygon) with streams (lines) and water usage wells (points).  All of these features have specific attribute information. 





In a GIS all of the features have information.  The information about the Centre County polygon is to the left. 


This table contains the demographic data, but it could also contain information on crime or politics related to Centre County.







 One of the advantages of a GIS is the ability to combine data from many resources—layer many themes.




This is a point theme of surface water supplies.




This is a line theme of rivers.




This is a polygon theme of the Pennsylvania county boundaries.



This example shows all three different themes can be layered into one.


Next is a demonstration of how to query the different data layers.






This is an example of a query.


The question is , What are the Surface Water Intakes that are within .5 miles of a river.




The features highlighted in yellow are all the points that are within .5 miles of a river.




When the surface water intake point is measured it is .33 miles from the river.







What is NOT a GIS:


GPS, which stands for Global Positioning System, is a device that enables you to show your exact position on Earth.  There are 24 GPS satellites that orbit 11,000 nautical miles above the earth.  The satellites are monitored by ground stations that are located throughout the world.  Satellites transmit signals that can be picked up by the GPS receiver and determine your location.


A GPS can be used to record location, which is represented in Latitude and Longitude coordinates.  Coordinates are stored in the GPS, and can be uploaded to a GIS to create thematic layers.


A static map, paper or digital



A software package is NOT a GIS


It is the way a person manipulates the software, not the software alone.  The user must be able to manipulate the data in order for it to be considered a complete GIS.



Why Use GIS?


GIS is a powerful tool for analyzing and mapping geographic data.   As mentioned above it is the combination of database operations (query, selection) and visualization tools that makes a GIS unique. 


Prior to GIS the development of GIS, it was extremely difficult to perfom queries that involved more than one or two layers of data.  The modern GIS makes it possible to quickly and easily query multiple layers of data and display the results in a thematic map or tabular report.  Whether you are a farmer and you want to find the best soil for growing corn, finding the best route for an emergency vehicle, or a realtor finding a house with three bedrooms, a GIS provides the tools to ask questions, explain events, visualize scenarios, planning strategies, to name a few.



GIS can be used to:


·       Explain events

·       Predict outcomes

·       Planning Strategies

·       Create “smart” maps

·       Integrate Information

·       Visualize scenarios

·       Solve complicated problems

·       Present powerful ideas



Who Uses GIS?


Police and Law enforcement

Emergency Response

Community Planning

Local and Federal Government


Health Industry


Environmental Engineers


Real Estate Professionals

Market Developers


Plus Much More!



How to Get Started Using GIS



PASDA Tutorials 


Training and Education 


How to get started in schools and Libraries  


Community Atlas Project—win free ArcView software 


Download ArcExplorer for free