Monthly Archives: January 2007

Spatial Thinking: Understanding Your Data

Think of spatial data as the fuel for your GIS engine.  It is fundamental to any spatial analysis.  On listservs, blogs, and in the ESRI Knowledge Base, discussions about data are commonplace.  The volume of spatial data available has increased dramatically as have the formats in which that data is stored, and the means by which that data is delivered to the user—via web-mapping services, servers, FTP sites, media, user-defined boxes and predefined tiles, and more. 

In this avalanche of spatial data, it is more important than ever to encourage students to fully understand the data they are using.  They tend to view anything on the computer as accurate and complete, including maps.  Maps are incredibly useful, but inherently full of errors and distortions, from the map projection, to missing data, to generalized lines.  Nowadays, anyone can make a digital map.  Help students understand that data quality affects subsequent analysis.  For example, in my lesson on plate tectonics (on http://www.esri.com/arclessons), I ask students to study 2001’s largest earthquake, below, at the arrow:

Students measure that the earthquake is 4 km off of the coast of Peru.  But then I ask them to consider the generalized coastline digitized at 1:30,000,000.  How confident are we that the earthquake was offshore?  Consider the length of the British coastline—the more detailed the scale, the longer the coastline becomes, because at larger and larger scales, it includes every cape and bay.  Peru’s coastline may actually twist and turn, so the earthquake could have occurred on the beach.  The “so what” and spatial thinking component continues with discussion of the impacts of coastal earthquakes versus underwater quakes. 

Encourage your students to be critical of spatial data—knowing its source, who produced it, when and why it was produced, the scale at which it was produced, and its content.   Show them how to create and access metadata.   They will then be able to critically evaluate spatial information and decide whether they will use it in their present and future decision making.

- Joseph Kerski, ESRI Education Manager

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