Archive for December, 2019

Download Arctic area digital elevation data from ArcticDEM

December 22, 2019 Leave a comment

Here we are at the winter solstice in the Northern Hemisphere and it seems appropriate to discuss polar data.  ArcticDEM is an NGA (National Geospatial Intelligence Agency) – NSF (National Science Foundation) public-private initiative to produce a high-resolution (2 meter), high quality, digital surface model (DSM) of the Arctic using optical stereo imagery, high-performance computing, and open source photogrammetry software.  The majority of ArcticDEM data was generated from the panchromatic bands of the WorldView-1, WorldView-2, and WorldView-3 satellites. A small percentage of data was also generated from the GeoEye-1 satellite sensor.  The resource covers all land north of 60 degrees north latitude.  Yes!  Not only Alaska, but Scandinavia, Russia, Canada and Iceland.  For more information, see this page.  For a web mapping application the Arctic DEM Explorer from Esri, see this page, and for the bare-bones but useful file index for fast downloading, see this page.

In my opinion, the most useful site about Arctic DEM for downloading the data is this web mapping application, the ArcticDEM index and data download.  This application allows a user to select specific index tiles of digital elevation model data.  The tiles reveal information about the DEM tile and a download web URL.  Each cell is about 2GB, with over 18 TB on the entire site.  Truly a treasure trove of data!  For selecting multiple indices, use the ‘Query’ tool to draw an area and return information on intersecting DEM tile indices. You can export these results for your reference which also include the download web URLs.

Click on any location for attribute information.  Find the “fileurl” attribute, click on More info, and then you will be able to download the 2 meter elevation data for that location.  The query widget allows for the retrieval of information from source data by executing an intersect query either against 2m DEM strips or 2M DEM mosaics.   The resource also includes a swipe tool where you can compare the content of two different layers on the map, such as the index layer and the hillshade.

The best news about this resource, and consistent with our continued mantra about GIS as a SaaS, may be that the site allows for the data to be examined as an ArcGIS Online item and also as an image service via a URL.


Interface of the Arctic DEM Index and Data Download resource. 


The Arctic DEM data streamed and viewed in ArcGIS Online. 

I look forward to hearing your reactions to this resource.

–Joseph Kerski

A Geodata Fabric for the 21st Century, article reflections

December 15, 2019 4 comments

A recent article by on A Geodata Fabric for the 21st Century touches on many pertinent themes in geospatial technology in this column and beyond.

Jeff begins by reminding us of the 4 V’s of big data–volume, variety, velocity, and variability, telling us that we are firmly in the age of big data, with the NISAR satellite soon to be providing 85 TB of data per day, as just one example.  But he also states that geospatial and earth science is not the only field grappling with big data, giving impressive numbers coming out from astronomy and geomics (geonome science).  Jeff says, “We need a more unified approach such that each data provider—whether in the atmosphere, land surface, seismology, hydrology, oceanography, or cryosphere domain—can contribute to a shared and commonly accessible framework.”  To build it, he says we need (1) a new type of storage (such as object storage); (2) minimize the number of times we move data (I think of how many times in a typical project I move data around:  Can I reduce this number?); (3) to take advantage of the cloud; and (4) keep things simple.  Jeff says, “A user should be able simply to ask for—or directly visualize—a desired data set, time range, and area of interest while software behind the scenes automatically provides what was requested.”  Amen to that!  And he makes a good tie to the role that machine learning could play.   Could the Esri geospatial cloud help enable this?

Taking a step back from the technological and logistical aspects of collecting and managing large volumes of data, we also need to ask what we want from all this data, in the short, medium and longer term. Our aspirations and expectations are sometimes harder to define and maintain. What do we want to do with all this data and when do we need to do it? There are many great examples of some of the things we can do with spatial data but sometimes they seem to focus more on the technology, the latest version of a particular software or innovation in data management technology, than on progress towards achieving a longer term goal such as improved environmental and resource management.

The improvements in data collection, storage and management over the last 50 years have revolutionised what we can capture and what we can do with the data. To make the most of these invaluable data assets, we must also avoid the distraction of the bright shiny lights of technology for technology’s sake and keep in mind what we are trying to achieve. Starting with the desired end result:  What data helps achieve that, the best source/format/currency, regardless of how it is stored and whose server does it sits on.

–Jill Clark, Joseph Kerski


Categories: Public Domain Data Tags:

Be a Wise Consumer of Fun Posts, too!

December 12, 2019 12 comments

Around this time of year, versions of the following story seem to make their way around the internet:

The passenger steamer SS Warrimoo was quietly knifing its way through the waters of the mid-Pacific on its way from Vancouver to Australia. The navigator had just finished working out a star fix & brought the master, Captain John Phillips, the result. The Warrimoo’s position was LAT 0º 31′ N and LON 179 30′  W.  The date was 31 December 1899.

“Know what this means?” First Mate Payton broke in, “We’re only a few miles from the intersection of the Equator and the International Date Line”.  Captain Phillips was prankish enough to take full advantage of the opportunity for achieving the navigational freak of a lifetime.  He called his navigators to the bridge to check & double check the ships position.  He changed course slightly so as to bear directly on his mark.  Then he adjusted the engine speed. The calm weather & clear night worked in his favor. 

At midnight the SS Warrimoo lay on the Equator at exactly the point where it crossed the International Date Line! The consequences of this bizarre position were many:  The forward part (bow) of the ship was in the Southern Hemisphere & the middle of summer. The rear (stern) was in the Northern Hemisphere & in the middle of winter.  The date in the aft part of the ship was 31 December 1899.  Forward it was 1 January 1900.  This ship was therefore not only in two different days, two different months, two different years, two different seasons, but in two different centuries – all at the same time.

I have successfully used many types of geographic puzzles with students and with the general public over the years, and I enjoy this story a great deal.  But in keeping with our reminders on this blog and in our book to “be critical of the data,” reflections on the incorrect or absent aspects to this story can be instructive as well as heighten interest. The SS Warrimoo was indeed an actual ship that was built by Swan & Hunter Ltd in Newcastle Upon Tyne, UK, in 1892, and was sunk after a collision with a French destroyer during World War I in 1918.  Whether it was sailing in the Pacific in 1899, I do not know.

The version of this story on CruisersForum states that it is “mostly true.”  What lends itself to scrutiny?  Let us investigate a few of the geographic aspects in the story.

First, the statement, “working out a star fix” leaves out the fact that chronometers were used to work out the longitude, rather than a sextant.  (And I highly recommend reading the book Longitude by Dava Sobel).  Second, the International Date Line (IDL) as we know it today was not in place back in 1899.  The nautical date line, not the same as the IDL, is a de jure construction determined by international agreement. It is the result of the 1917 Anglo-French Conference on Time-keeping at Sea, which recommended that all ships, both military and civilian, adopt hourly standard time zones on the high seas. The United States adopted its recommendation for U.S. military and merchant marine ships in 1920 (Wikipedia).

Third, the distance from LAT 0º 31′ N and LON 179 30′ W to LAT 0º 0′ N and LON 180′ W is about 42 nautical miles, and the ship could have traveled at a speed of no more than 20 knots (23 mph).  Therefore, conceivably, the ship could have reached the 0/180 point in a few hours, but whether it could have maneuvered in such a way to get the bow and stern in different hemispheres is unlikely, given the accuracy of measurement devices at the time.  Sextants have an error of as at least 2 kilometers in latitude, and chronographs about 30 kilometers in longitude. Or, they could already have reached the desired point earlier in the day and not have known it.  Even 120 years later, in my own work with GPS receivers at intersections of full degrees of latitude and longitude, it is difficult to get “exactly” on the desired point:  Look carefully at the GPS receiver in my video at 35 North Latitude 81 West Longitude as an example.  An interesting geographic fact is that, going straight East or West on the Equator along a straight line, it is possible to cross the dateline three times (see map below).

Our modern digital world is full of fragments that are interesting if not completely accurate, but as GIS professionals and educators, I think it is worth applying “be critical of the data” principles even to this type of information.  The story is still interesting as a hypothetical “what could have happened” and provides great teachable moments even if the actual event never occurred.


The International Date Line (CC BY-SA 3.0,

New free course on teaching and learning with the ArcGIS Living Atlas of the World

December 8, 2019 Leave a comment

I am very pleased to announce that the course that my colleague and I created on Teaching with ArcGIS Living Atlas of the World is now available!

The course is:  Free, fun, and rigorous!  It provides skills and perspectives for making effective use of the wonderful resources that are in the Living Atlas in teaching and learning.  We first wrote about the Living Atlas on this blog, here.  Yes, the course is geared toward educators, but could be useful for non-educators who love data, as well.

–Joseph Kerski

livatl.PNGFront page to Living Atlas course.