Introduction to GIS

Caitlin Dempsey


The fundamentals of GIS involve an understanding about data types, projections, data quality (accuracy and precision), how to collect data and elementary spatial analysis, exposure to geospatial technology/terminology, types of GIS data, data sources, and methods of obtaining data, basic cartography, types of spatial analyses and when to use them.

Listed here is an outline covering the topics listed about with further links on GIS lounge to help you develop a foundation to the basics of GIS.

Introduction to GIS

Ask ten different people “what is GIS?” and get ten different explanations.  The definitions of a GIS have evolved in different areas and disciplines. What all GIS definitions have in common is the recognition that spatial data is linked to maps (space matters!). At its most basic defintion, a GIS at least consists of a database, map information, and a computer-based link between them.

What is GIS used for?

GIS has many real world applications.

GIS is used to develop and store geographic and attribute data.

Geographic analysis which looks at spatial distributions of lands, people and resources and attempts to explain and predict not just describe.  Geographic analysis also looks at what impacts patterns have on health and well-being of both people and environments.

Criteria matching by querying different geographic data sets to answer real world questions.  For example, being able to find all schools located at least 1000′ from a highway, within 200′ of a bus stop, and within 1 mile of a park.

Exploration of  spatial relationships among data layers.  John Snow’s malaria map is a classic example of mapping out geographic data in order to understand the relationship of a contaminated water pump with the spread of disease.

GIS serves as a data handler for other analyses.  For example, passing geologic and topographic data to an erosion model of the Appalachians, or passing water quality and groundwater levels to a groundwater flow model; these are typically written programmatically that can access the GIS.

GIS aids visualization which improves understanding and pattern recognition, facilitates public participation in alternative scenarios, and helps coordinate group decision making.

Subsystems of a GIS

  • Data input subsystem: preprocessing, transformations
  • Data storage and retrieval subsystem: organizes for retrieval, editing, updating
  • Data manipulation and analysis subsystem: aggregation, dis-aggregation, modeling
  • Reporting (output) subsystem: output (tabular, graphic, map…)

GIS Data

Almost all human activity and natural phenomena are spatially distributed and therefore can be studied within a GIS.  The standard GIS data model represents a landscape using four types of features: points, lines, areas or surfaces.

For more on GIS data: GIS data explored, Basic Geographic ConceptsGIS Data: A Look at Accuracy, Precision, and Types of Errors, and Metadata.

How to create data?  See: Methods for creating spatial databases, Data Capture in GIS, Digitizing Errors in GISOrthophotos and GIS.  


A database is a collection of data files that is structured (organized) to facilitate data storage, manipulation, and retrieval.
A database management system (DBMS) is a software package that performs these database functions.

Spatial Analysis

  • Location …Where is it?
  • Condition …What is it?
  • Patterns … How is it distributed?
  • Trends …What has changed?
  • Modeling … What if …?
  • Time and Travel?
  • What is near me?

More: Spatial Analysis in GIS

Map Basics

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.

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