Monthly Archives: May 2011

Analyzing the Mean Center of Population for the USA and States

Analyzing the Mean Center of Population for the USA and for Individual States, Updated for ArcGIS 10 and Census Year 2010

A new lesson, entitled “Population Drift: Mean Center Analysis 1790-2010” in the ArcLessons library (search on Population Drift), invites students to use spatial analysis, spatial statistics, and GIS to determine and analyze the population centers of the USA and individual states over space and time, from 1790 to 2010. This lesson was recently updated to include 110 in-depth questions, a very rich set of data including the new 2010 county population figures, and to use the powerful spatial statistics tools in ArcGIS 10.

The objectives of this lesson are to 1) Understand the definition of and application of mean center and weighted mean center; 2) Understand the definition and use of a population weighted mean center in a GIS environment; 3) Learn how to calculate mean population centers for the USA and for individual states using GIS tools; 4) Understand the magnitude and direction of movement and key reasons why the US population center moved from 1790 to 2010; and 5) Analyze how and key reasons why population centers for individual states moved from 1900 to 2010. Skills include calculating mean centers, selecting and using spatial and attribute data, and symbolizing and querying maps. The investigation of population change and population centers naturally lends itself to discussions of job creation and loss, economic conditions, perceptions of place, the evolution of agribusiness and rural outmigration, urbanization, suburban sprawl, sunbelt migration, changes in the median age, changes from industry to services, international migration to the USA, and a whole host of other issues. Examining the population center for individual states allows students to consider how these issues operate on a state scale.


The Census Bureau recently published information on the location of the new 2010 USA center of population, as well as a series of interactive maps showing the 1790-2010 movement, on: http://2010.census.gov/2010census/data/center-of-population.php.
Linked to the page is a series of videos from Census Bureau Director Robert Groves who discusses the movement of the population center. These interactive maps and videos provide excellent supplementary materials to the ArcGIS-based lesson.

How might you use this lesson to teach about the many economic, political, demographic, and perceptual forces operating over the decades?

-Joseph Kerski, Education Manager

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Fun with GIS #85: Feds Say GIS is STEM

Zounds! Feds declare GIS is STEM! This may be the biggest non-surprise since gravity, but it’s an important point. The US Immigration and Customs Enforcement issued a list of science, technology, engineering, and math (or STEM) degree programs that now specifically includes “Geographic Information Science and Cartography” among other additions. These changes will allow various high tech sectors to attract more foreign grads.



This news should also help convince many STEM folks in K-12 schools that geospatial technology does belong in their activities. Curiously, many educators with whom I’ve spoken were surprised by the notion of GIS as STEM, and many so-called STEM schools have skipped geospatial technology in their programs. The Geospatial Technology Competency Model should help clarify that.



Are there jobs in the geospatial realm? O*Net Online (sponsored by the US Dept of Labor/Employment and Training Administration, or USDOL/ETA) shows the outlook for geospatial jobs as both “bright” and “green.” What more can a school want? For CTE programs and others in STEM seeking a way to start, check out the instructional resources from Digital Quest. For more about careers in GIS, see the Esri EdCommunity Careers page.

- Charlie Fitzpatrick, Co-Manager, Esri Schools Program

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Analyzing the Spatial and Temporal Aspects of Tornadoes Using GIS

Spring in North America brings not only new flowers, but a new crop of tornadoes. The 2011 tornado season has already been horrific, and our hearts go out to all those affected. Like most natural phenomena, tornadoes exhibit a spatial pattern on a global, regional, and local scale, and a temporal pattern depending on season, time of day, and duration. Both the spatial and temporal components can be examined and understood with the use of GIS.

To do this, I have written three lessons and compiled data sets that may help do just that. The first, Investigating Historical and 1 Modern Tornado uses ArcGIS Online (http://www.arcgis.com, search on “Tuscaloosa owner:jjkerski”) to examine pre- and post-tornado imagery that can be toggled on and off or adjusted in terms of opacity. Using these sobering data sets, the width and length of the Tuscaloosa tornado can be examined, as well individual building types affected, and historical tornadoes by decade throughout the USA. The second, “Investigating Historical Tornadoes Using ArcGIS”, allows for further investigation, which reveals that while more common on the Great Plains and interior lowlands, tornadoes have occurred in nearly every state, and are not as uncommon in the mountain west as one might think. Contrary to popular opinion, the data also reveals that Kansas is not the area with the highest density of tornado outbreaks. Do you know what state has the highest density? See below.

Selecting the tornadoes by month shows the seasonal ebb and flow of the outbreak of tornadoes, starting from coastal areas near the Gulf of Mexico in January and increasing to a spatial maximum in July of each year. The numeric maximum occurs in April, three months earlier than the spatial maximum. During which six hour period do you think the most tornadoes touch down—between midnight and 6:00am, 6:00am to Noon, Noon to 6:00pm, or 6:00pm to midnight? Examining the historical data reveals that the tornado causing the most injuries (1,740) occurred in northern Texas in 1979 and the one causing the most fatalities (116) occurred in northeast Michigan in 1953. The lesson also invites you to discover in which elevation range tornadoes are most common, and the difference between tornado touchdowns and tornado tracks.

The third lesson invites students to download and analyze a single day of tornadoes. Using data from the NOAA Storm Prediction Center, the lesson begins with an analysis of 22 April 2011, the day of the tornado that caused damage at the St Louis airport. Analysis reveals that the airport tornado was only one point along a line of tornadoes that day in that region. Wind and hail for that day are also analyzed, including the determination of the mean center and standard deviational ellipse for all storm types. The lesson concludes with the students’ selecting a different day, downloading the CSV files from NOAA, and mapping and comparing them to 22 April’s storms.


-Joseph Kerski, Education Manager

Answer: According to this dataset, tornado density is highest in sections of Oklahoma.

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Fun with GIS #84: ArcGIS.com Presentations

Geopresentations on an iPad! Or any other device using ArcGIS.com Map Viewer, the “one-foot high jump” intro to GIS. From its birth a year ago, ArcGIS Explorer Online has been able to create presentations (see Fun With GIS #80), but they were originally available for viewing only on the same tool. Since Explorer Online uses the Microsoft Silverlight browser plugin, full Macs and PCs could make and view presentations, but iPads could not. Now, however, the ArcGIS.com Map Viewer can read and play these presentations. It’s a great asset, as presentations can now play on any Javascript-capable browser, including smartphones and tablets, and school labs lacking plugins.

To demo, I steered my iPad to ArcGIS.com and typed “communityatlas” (all one word) in the search window.

Two options appeared, so I clicked the “WashDC” version, and went to an ArcGIS.com Map Viewer display. Over on the left, there is a new choice: “View Presentation”

When clicked, this launches a new browser window, with controls at the bottom. Users have full control to pan and zoom (including pinch/spread on iPad), and wander back and forth between frames.

Because users of ArcGIS Explorer Online can build any number of projects, with lots of intro GIS experience embedded, this is a tremendous development that will help new users grasp key concepts and skills that are crucial for GIS, while learning solid STEM (including social studies) content.

- Charlie Fitzpatrick, Co-Manager, Esri Schools Program

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Scale Matters, 2 of 2

Scale Matters, 2 of 2

Several types of scale exist in geography. Cartographic scale refers to the size of a feature on a map relative to its actual size in the real world. Cartographic scale can be expressed as a verbal statement such as “one inch equals one mile”, or graphically as in a scale bar, or as a representative fraction, such as 1:24,000 scale. A small scale map (such as 1:1,000,000) shows a great amount of area but not much detail. A large scale map (such as 1:24,000) shows a great amount of detail but not much area. This may seem counterintuitive but it is because the ratio 1:1,000,000 (or 1/1,000,000) is smaller than 1/24,000. A small fraction means a small scale map. Confusion sometimes occurs because when we discuss large scale phenomena, we usually are referring to things operating over a large area, like hurricanes. But if we were to map all of the hurricanes in a year over the North Atlantic, the map would actually have to be at a small scale to see them all at once. To clarify, I often use the terms “fine scale” and “coarse scale.”

Analysis scale refers to the size of the unit at which a particular problem is analyzed, such as on a scale of a watershed or neighborhood. Phenomenon scale, as referred to by UCSB’s Daniel Montello, is the size at which human or physical earth structures or processes exist, regardless of how they are studied or represented. They are interrelated. For example, choices concerning the scale at which a map should be made depend in part on the scale at which measurements of earth features are made and the scale at which a phenomenon actually exists.

Therefore, scale is important far beyond the map. It is important in deciding at what scale to analyze a problem. For example, for analyzing river systems, is it most appropriate to study whole drainage basins, or select a sample of watersheds? For languages, should you study dialect areas or whole language regions? We often use terms such as local, micro, meso, macro, and global in discussing scale. The idea of nesting is also important – blocks nest inside block groups, which nest inside census tracts which nest inside counties for US demographic analysis based on US Census Bureau geography. Sometimes we have to generalize features and phenomena to really see the pattern, simply because there is too much detail at a local level, and so generalization has to do with scale as well.


I discuss all of this in a video on: http://esriurl.com/scalematters. GIS contains many functions that can be effectively used in teaching about scale. How might you use GIS to teach about scale?

-Joseph Kerski, Education Manager

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Fun with GIS #83: Discovery with Landsat

Change matters! 30 years of Landsat photos are now easy to view on Esri’s Landsat website. The data can be explored with just a web browser, even on an iPad!


It’s tempting to jump right in and begin using the first application that shows up, but be sure to hit the “Tours” link at the top. Even if you don’t see all the amazing tours in place, see at least the first one, on “ChangeMatters Tips.”


The tour, shown below on an iPad, walks users through some of the important opportunities and considerations in using this remarkable collection (over 8 terabytes!) of images. This example engages the “Explore” application, which can also be used independent of tours, and shows a single window.


The “Compare” application (again, shown on an iPad) presents a region at two different times, with the third panel showing the difference. Below, you can see the Aral Sea shrinking between 1975 and 2000.


All the data can also be used with ArcGIS.com MapViewer, ArcGIS Explorer Online, ArcGIS Explorer Desktop, and ArcGIS Desktop, each of which opens up more and more power for users to explore and analyze conditions and change over time. These powerful applications provide countless lessons in science and social studies, show beautifully the integration of remote sensing and GIS, and help demonstrate why geospatial technologies are so important in STEM classes and offer such vast career opportunities to today’s youth.

- Charlie Fitzpatrick, Co-Manager, Esri Schools Program

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Scale Matters, 1 of 2

Understanding geography and using GIS as an analytical tool in education and research requires a sensitivity to and an awareness of scale. This provides a framework for understanding how events and processes influence each other. Any phenomena we are studying at one scale can be influenced by phenomena operating on other scales. For example, traffic patterns affect local neighborhood zoning and movement, but also affect regional land use and reflect regional patterns of trade. They also reflect and can be studied in the context of national or international migration, economics, and demographic characteristics. Climate is another complex phenomenon that operates at multiple scales. It affects weather on a local scale but also affects such global phenomena such as ice pack at the poles, sea level, and the location of deserts, rainforests, monsoons, and consequently, human settlement, agriculture, clothing and building styles, and much more. In between, at a regional scale, climate is affected by landforms, such as mountains, prevailing winds, and even eruptions of volcanoes. Thus, to fully understand our complex world, we must look at processes across multiple scales.

Scale is about size. It can be relative or absolute. Scale can be about space, or about time, since things that occur across space almost always have a temporal component. For example, think about wildfires versus glacial advance. They have different spatial scales and different temporal scales. There is also a thematic scale, having to do with the grouping of attributes such as water quality or weather variables.
Scale is a theme that runs through all of geographic analysis, because geographic analysis has to do with trends, patterns, relationships across space and, often, time as well.

Consider the different processes operating on this landscape on a local scale, photographed on the ground, versus those operating at a regional scale, photographed out an airplane window of the same location.

Several types of scale exist within geographic analysis. They are interrelated and are equally important. They are also important far beyond geography, in any discipline where spatial aspects are considered, such as in epidemiology, biology, earth science, or business marketing. GIS can be used in a wide variety of ways to teach about each type of scale, which I discuss in a video on: http://esriurl.com/scalematters. I will discuss the different types of scale in the next blog.

How might you use GIS to teach about scale?

- Joseph Kerski, Education Manager

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Landsat is here!

Want to see change in the landscape over time, from 1975-2005? Head to www.esri.com/landsat and work with the “ChangeMatters” application. Or add the services into your activities with various GIS apps!


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