Projections

GIS contains spatial data (unlike other information systems).  Spatial data includes coordinates that define geographic objects.  Geodesy was mentioned in the last post. Geodesy is “the science of measuring the shape of the Earth (Bolstad).”  Because it’s hard to perceive the curvature of the Earth on a human scale, we’ve been using flat maps for the majority of our lifetime.  Flat maps distort geometry due to not being able to take into consideration the curvature of the Earth.

A flat map complicates defining coordinates because measurements are affected by the distortion created by flat maps.  The irregular shape of the Earth and imperfect measurements also complicate the defining of coordinates.  Earth is not a perfect sphere shape and is actually very deformed because of natural forces.  Our measurements contain error but with improvements over time and with the sophistication of models, our measurements of positions on Earth improve.

All these differences in defining coordinates cause us to create “several sets of coordinates that define the same location on Earth (Bolstad).”  The points created at a location on Earths’ surface are coordinates that depend on how the points from a flat map are translated onto a curved map surface, what type of reference is used in creating the coordinates and what shape of the Earth is taken into consideration when formulating the measurements for the points.

 

 

Reference:

 

Bolstad, Paul. (2012).  GIS Fundamentals:  A First Text on Geographic Information Systems.  White Bear Lake, MN:  Eider Press.

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Another Introduction to GIS

There are several definitions used while explaining geographic information systems (GIS).  One of the most popular definitions for GIS is “a computer-based system to aid in the collection, maintenance, storage, analysis, output, and distribution of spatial data and information. (Bolstad)”  GIS helps us gather and use spatial data;  it is concerned with absolute and relative location of features (the where) and it’s concerned with properties and attributes of those features (the what).

GIS quantifies locations by recording their coordinate positions on Earth (latitude/longitude).  GIS tools are essential in business, government, education, and non-profit organizations (Bolstad).  It helps us identify and address environmental problems by providing information on where the problems occur and who are affected by them.  Using GIS we are able to identify the source, location, and extent of environmental impacts.

Advances in three key technologies have helped aid in the development of GIS; imaging, GNSS, and computing.  Cameras these days provide detailed aerial and satellite images, images can be easily converted to accurate spatial information over broad areas.  Global Navigation Satellite Systems (GNSS) is a positioning technology that’s now incorporated in cars, planes, boats, and trucks. Powerful field computers are now lighter, faster, more capable, and less expensive, allowing spatial data display and analysis capabilities to always be at hand.

Geographic information science (GISci) includes the technical aspects of GIS as well as seeks to redefine concepts in geography in the context of the digital age, making GIS dependent on GISci.  GISci not only investigates technical questions but also explores more basic questions, such as, “How might we best represent spatial concepts? (Bolstad)”

 

 

Reference:

 

Bolstad, Paul. (2012).  GIS Fundamentals:  A First Text on Geographic Information Systems.  White Bear Lake, MN:  Eider Press.