Monthly Archives: April 2011

Analyzing Change Over Time Using Topographic Maps and Imagery with GIS

A principal aim of geospatial analysis is examining and understanding change over space and time. One of the simplest yet most powerful things you can do in ArcGIS desktop ( or in ArcGIS Online ( is to visualize change over time by studying change based on different basemaps created on different dates.

For example, I recently conducted a GIS workshop for educators at Northeast Junior College in Sterling, Colorado. While on campus, in ArcMap, I added satellite imagery as well as the USGS topographic map. I determined the date of the topographic map (1971) by accessing the USGS Map Store. I found the date of the satellite imagery (2009) by using the Identify tool in ArcMap on the imagery layer. I used the swipe tool so I could scroll back and forth across the map to easily compare the different basemap images.

The nearly 40 years of changes revealed by comparing the topographic map to the satellite imagery indicated that the name and the location of the college had changed. The college had changed from Sterling Junior College to Northeastern Junior College, and had expanded from the northeast to the southwest. The current location of the college is the former Logan County fairgrounds. After mapping the route we took during our fieldwork with GPS receivers that day (shown in dark yellow on the map below), we discovered that we were on the old fairgrounds track. We could trace the fairgrounds track and then walk that same route on the current campus, noting what had changed.

Comparing the two basemaps revealed changes beyond the campus, including the direction that Sterling had expanded over the decades, the expansion of commercial zoning into former residential areas, and even the renumbering of the interstate from I-80S to I-76. In ArcMap, we measured the areal extent of the city in 1971 and today, compared the percentage of expansion to other communities in the area and other communities of a similar size in the region, and examined population data of these communities.

How might you analyze change over time using topographic maps and imagery of an area you are interested in?

-Joseph Kerski, Education Manager

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Free Webinar: Fast and Fun Geo-Web 2.0 Activities for End of the School Year

May 11, 2011 at 9pm EST/8pm CST

Dr. Joseph Kerski presents web-based GIS ideas that you can use in the classroom tomorrow! Explore engaging, one-day, classroom activities that use cutting-edge Geo-Web 2.0 tools. We’re highlighting the web-based mapping tools that will inspire students to learn, even with the last days of school fast approaching. Join Dr. Joseph Kerski, 2011 NCGE President and an Esri Education Manager as he leads this webinar. The face-paced, intriguing nature of the Geo-Web 2.0 Tools will be sure to turn your students’ minds to learning before they can grab their flip flops and plan their summer vacations. Don’t miss it!

Register online now!

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Texas Wildfires and Texas Map Society Meeting

Later this week, my wife and I are attending the Texas Map Society spring meeting being held in Alpine and Fort Davis, TX. It promises to be a great blend of historical and 21st mapping discussions as well as archeology and natural history, and it’s in a part of the country we have never visited before. As I mentioned it to a colleague, he asked if there were any wildfires nearby as Texas fires are in the news every day right now. Good question. The answer we discovered is “yes.”

Using a new interactive Esri wildfire map, we were able to check out the activity across the state and most especially the area around these two West Texas towns. The statewide view showed a lot of fire activity and currently little rain to dampen the problem.

Zooming into the Alpine-Fort Davis area provided much detail including the ignition point near Marfa of what’s called the Rock House fire that as of April 25 involved nearly 225,000 acres. Turning on the wildfire perimeter layer gave a sobering picture of just how extensive this fire is/has been, including Fort Davis where the YouTube and Twitter links are located. As shown below, the map also gave a picture of where active hotspots are located inside the northwest perimeter.

Since part of Society’s events will happen at the Davis Mountains State Park I zoomed in again for a closer look, and yes the park itself has been subjected to fire and according to the park web site is currently closed. (Hmmm, wonder how that will change things for the meeting?)

With the main portions of the multi-day event happening at Sul Ross State University and other venues in Alpine, I found myself also curious about fire potential in the vicinity. The current status indicated is “moderate” danger.

So, what has seemed like something only visible on the nightly news here in Texas may soon become a first-hand experience for me. I’m certain that the Society sessions and discussions will include a new focus, and with 21st century geographic tools like this we’ll be able to stay in touch with the big picture while we travel the local landscape.

- George Dailey, Esri Education Program Manager

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Fun with GIS #82: Anticipating Landsat

Landsat is coming! Esri is preparing terabytes of data for access thru ArcGIS Online. Earlier this year, Esri Federal User Conference and Esri Partner Conference audiences saw sneak previews. You can check out the coming access by watching a few minutes of video. Click the graphic below and scroll down the transcript to 3:13, then watch the segment from 3:13-6:58.

As the movie shows, Landsat data in ArcGIS Online will allow educators and students to see change over time from 1975-2005, in your choice of application: specific web browser app, Map Viewer (including on iPad), ArcGIS Explorer Online, ArcGIS Explorer Desktop, or ArcMap. You’ll be able to overlay layers and conduct analyses against them. See the effects of climate change, urbanization, deforestation, but also the occasional re-establishment of native habitat. These will be powerful capacities for social studies, earth science, and other STEM classes.

- Charlie Fitzpatrick, Co-Manager, Esri Schools Program

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Comparing a GPS vs. SmartPhone, Part 2 of 2

Recently, I wrote about my comparison of the horizontal position obtained from a consumer-grade GPS receiver versus that obtained on a SmartPhone. Specifically, I compared a Garmin GPS 76 to an iPhone 4. The position recorded on my iPhone was consistently tens-of-meters off from the position recorded with my GPS receiver. Thus far, it appeared that my position as recorded by my GPS receiver is far more accurate than that from my iPhone. However, this was not the end of the story.

In the field, I switched to the map view on my phone, and the blue dot marking my current position was not hundreds of meters away, but just a few meters from where I was standing. I took a photograph here and emailed it to my PicasaWeb account using the procedures I wrote about in a previous blog column.

This photograph was geotagged at 39.680000 north latitude, 104.962667 west longitude, which turned out to be only 6.21 meters away (this time to the southwest) from my position as recorded by the GPS receiver. Interesting! This means that the SmartPhone was indeed recording an accurate position, but perhaps the app used to capture that position may have compromised that position.

The map I created from ArcGIS Explorer Online below shows my hyperlinked photograph very near to the position where I conducted the experiment, and several blocks to the northwest is the position recorded by the default compass utility in my phone.

Zooming in, Pushpin A at the end of the green line points to where I stood at the brick wall on campus. Pushpin B, 5.23 meters north-northwest, is the position recorded with my GPS receiver, and Pushpin C, 6.21 meters to the west-southwest, is the geotagged position recorded in the photograph I took at that spot.

Your results will vary with the tools, including the types of WebGIS, GPS, and SmartPhone used. For example, a higher-end GPS such as a Trimble or TopCon will surely provide better horizontal accuracy. Also, would my iPhone position have been any better if I had used a GPS app instead of the default compass tool in my phone?

All of these technologies will continue to undergo rapid change, providing ample opportunity for further experiments. These types of experiments connect mathematics, GIScience (including discussion on datums, coordinate systems, and data quality), and geography. How might you turn these activities into teachable moments and activities?

- Joseph Kerski, Education Manager

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2011 Earth Day PollMap

Help us observe Earth Day 2011 by letting us know what you think are the most important environmental challenges facing humankind.

Imagine you had $100 to spend to help protect the Earth. How would you invest your money?

  • Climate Change & Sea-level Rise
  • Sustainable Alternative Energy
  • Population Growth and Family Planning
  • Unpolluted Air and Fresh Water
  • Healthy and Sustainable Food Supplies
  • Environmental Education
  • Clean Oceans and Sustainable Fisheries


Vote now!

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Fun with GIS #81: AGX Shows Where Matters

“Is geospatial tech useful to instructors of all fields in community colleges?” That was the question I sought to answer in a speech to several hundred instructors from Virginia last week. The subtitle for the talk was “Where Matters,” with apologies to English teachers for a purposefully ambiguous phrase.

While my recent blogposts have emphasized web-based tools, for this task I chose ArcGIS Explorer Desktop (“AGX”), for its flexibility, power, and presentation capacity. What a powerful tool this is!

I created notes linked to external or local web pages, pdf files, images, and movies. I used local shapefiles and layer files, plus downloaded layer packages. I used a banquet of online web services by themselves or with image files of legends. I meandered across the planet, exploring data, applications, problems, analyses, and strategies for thinking about a few of the countless issues of today, using the exploding repositories of data. Finally, I captured the frames ahead of time and built a doc to run on my iPad with a few notes to keep me on track.

AGX is much more powerful than the strictly web-based apps I’ve emphasized in “Fun with GIS” # 49-80, and takes more getting used to. But it is a perfect “three-foot high jump” to come after the “one-foot high jump” of Map Viewer and “two-foot high jump” of ArcGIS Explorer Online. Students and educators who have mastered the web-based tools and yearn for more power (on a strong computer running Windows) should look here for the next step. Search for ArcGIS Explorer lessons in ArcLessons, check out the AGX Resource Center (especially the blog), and look for “20 Minute GIS” from GIS ETC for a set of classroom activities using AGX. Help other students and educators discover why “where matters.”

- Charlie Fitzpatrick, Co-Manager, Esri Schools Program

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Comparing a GPS vs. SmartPhone, Part 1 of 2

Recently I wrote about techniques to use photographs taken on a SmartPhone as hyperlinks to locations where you have collected field data using ArcGIS Online as your mapping platform. These photographs are geotagged with a latitude-longitude coordinate recorded at the time and location that the photograph is taken. But how accurate are those coordinates, and how do they compare to the accuracy of locations recorded by a GPS receiver? In other words, do I really need my GPS receiver any longer, since modern SmartPhones can capture positions using an embedded GPS chip and even supplement the GPS position by triangulating off cell phone towers?

To find out, I recently conducted an experiment at a location I knew would be easily identifiable on a satellite image at the University of Denver. I compared the latitude and longitude positions gathered from a Garmin GPS 76 to those from an iPhone 4. My GPS dates from 2004 while my iPhone dates from 2010. The iPhone 3G, iPhone 3GS, and iPhone 4 models use A-GPS — or “Assisted GPS” — which in basic terms accesses an intermediary server when it is not possible to connect directly via satellite — indoors, for example — and this server provides the nearest satellite with additional information to make it possible to more accurately determine a users position. Also, the iPhone 3G, iPhone 3GS, and iPhone 4 also use “wi-fi hotspots and cellular towers to get the most accurate location fast” when GPS is not the most convenient method of location detection.

At the time of the experiment, my Garmin GPS 76 was reading 9 satellites and gave a horizontal accuracy of 4.38 meters (14.4 feet), with a latitude of 39.68006 degrees north and a longitude of 104.96262 degrees west. My iPhone gave me a position of 39.681944 degrees north and 104.965556 degrees west. The iPhone coordinates were more precise than those from my GPS receiver—they included more significant digits (6) to the right of the decimal point than the GPS included (5). But were the iPhone coordinates more accurate than that from the Garmin GPS receiver?

Learn more about geo-tools and the iOS: EdComm Geo-apps and iPhones | iPhones for geo-enabling your classroom | Esri’s iOS development SDK

I mapped these two coordinates using ArcGIS Explorer Online with an imagery basemap. Using the measure tool, I determined that the GPS location was 5.23 meters away from my “true” position based on the satellite image. This assumes that the satellite image is “correct”, but remember that imagery is not perfect either, and what is considered “correct” is a subject worthy of further discussion in a different blog column.

The position recorded on my iPhone was 333 meters away from my position as identified on a satellite image. Multiple experiments and then a summary of the results would be proper. At the time of this writing, I only had time to conduct one other experiment, 200 kilometers away, at Northeast Junior College in Sterling, Colorado, where I was teaching GIS and GPS. At that location, my iPhone coordinates were 40 meters off and my Garmin GPS coordinates were 5 meters off from my position as identified on a satellite image base map. Therefore, given these two experiments, I would conclude at this point that yes, my position as recorded by my GPS receiver is far more accurate than the position as recorded on my iPhone.

However, this was not the end of the story, as I will explain in my next blog entry.

- Joseph Kerski, Education Manager

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Geospatial Higher Education in Europe: AGILE

Learn about the Association of Geographic Information Laboratories for Europe and how the organization’s activities can inform your work.

The Association of Geographic Information Laboratories for Europe (AGILE) was established in 1998 to promote academic teaching and research on GIS at the European level and to ensure the continuation of the networking activities that have emerged as a result of the EGIS Conferences and the European Science Foundation GISDATA Scientific Programmes.

AGILE seeks to ensure that the views of the geographic information teaching and research community are fully represented in the discussions that take place on future European research agendas. AGILE also provides a permanent scientific forum where geographic information researchers can meet and exchange ideas and experiences at the European level.

Download the April 2011 AGILE newsletter.

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Summer GIS Workshop for Educators – Teaching with Spatial Technology (TwiST) 6/28-6/30

Want to engage your students in activities that will have them asking questions and thinking critically about content you cover in your educational environment? At the Teaching with Spatial Technology Workshop (TwiST), K-12 and college educators will learn how to teach with ArcGIS, GPS and other geospatial technologies in their educational environments. Participants will collect and gather data for a community mapping project while learning how to connect to state standards.

Celebrating its 10th year, TwiST will be held June 28-30, 2011 at Cayuga Community College in Auburn, NY. Registration is $250 before May 3 ($275 after May 3). The fee includes: 3-days of training, lunch, a notebook of materials, data, the opportunity to obtain an discounted geospatial software and tools, and approximately $1,000 worth of additional GIS learning resources. Both Graduate and Undergraduate credit is available for an additional fee.

The registration deadline for TwiST is May 3 for the discounted rate. Visit for registration and additional information.

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