Archive

Archive for January, 2017

A Top 10 List of Useful Geospatial Data Portals

January 29, 2017 6 comments

We have been writing this geospatial data column since 2012, when our book The GIS Guide to Public Domain Data, was published.  Over the 5 years that have elapsed, in addition to keeping issues such as data quality, copyright, privacy, and fee vs. free at the forefront of the conversation, we have tested and reviewed many geospatial data portals.  Some of these portals promise more than they deliver, some have been frustrating, but some have been extremely valuable in GIS work.  We have decided to list 10 of those that we have found most useful, rich with content, easy to use, and with metadata that is available and understandable.  In considering such a list, we realize that “most useful” really depends on the application that one is using GIS for, but the following sites should be useful for users in many disciplines. Some allow for data to be streamed from web servers into your GIS software, and all allow data to be downloaded.

  1.  The FAO GeoNetwork.  This portal contains global to regional scale data from administrative  boundaries and agriculture to soils, population, land use, and water resources.
  2.  The Esri Living Atlas of the World is an expanding, curated set of data and maps on thousands of topics that can be used and also contributed to by the GIS community.
  3. The European Space Agency’s Sentinel Online data portal includes a wide variety of image-related data sets on the five themes of land, marine, atmosphere, emergency, and security.
  4. CIESIN at Columbia University has been serving data for over 20 years on climate, population, soil, econonics, land use, biodiversity, and other themes, including its Socioeconomic Data and Applications Center (SEDAC).
  5. The Global Land Cover Facility at the University of Maryland remains one of the best and easiest to use sources and methods to obtain Landsat, MODIS, Aster, SRTM, and other satellite imagery.
  6. The Atlas of the Biosphere serves global data, largely in grid format, of human impact, land use, ecosystems, and water resources themes.
  7. Natural Earth is a public domain dataset at small scale (1:10,000,000, 1:50,000,000, and 1:110,000,000) for the globe, in vector and raster formats that are easily ingestible in GIS software.
  8. The World Resources Institute hosts a variety of data geospatial data sets for specific areas of the world, such as Kenya and Uganda.
  9. The GIS Data Depot from the GeoCommunity is one of the oldest data depositories, dating back to the 1990s, but still very useful for international and USA specific data on such themes as elevation, transportation, imagery, scanned topographic maps, and hydrography, many of which have been re-served from more-difficult-to-use government sites.
  10. There have been many “lists of data sites” over the years, and these invariably are not kept up to date and end up being less useful over time.  However, those that are still quite helpful that we have reviewed are Dr Karen Payne’s list from the University of Georgia, and Robin Wilson’s list of free spatial data.  A few others that are useful are this list from the USGS that I started back when I worked there, and this list from Stanford University.

A few selected others are also useful that “almost make the top 10” above are  The National Map from the USGS, data.gov from the US Government, environmental and population data from TerraPopulus, Diva-GIS’s data layers for each country, the UNEP Environmental Data Explorer, the NEO site at NASA Earth Observations, and OpenStreetMap.

For more details on any of these resources, search the Spatial Reserves blog for our reviews, remain diligent about being critical of the data you are considering using, and as always, we welcome your feedback.

landsat8_1

A Top 10 List of Useful Geospatial Data Portals.

Advertisements

Sharing Geoprocessing Tools on the Web

January 15, 2017 3 comments

An article co-authored by Benjamin Pross, Christoph Stasch, and Albert Remke, of the 52°North Initiative for Geospatial Open Source Software GmbH; and Satish Sankaran and Marten Hogeweg of Esri describes a development that should interest anyone who uses geospatial data.  The 52°North Initiative for Geospatial Open Source Software has developed an open-source extension to ArcGIS for Desktop that enables access to Open Geospatial Consortium, Inc. (OGC), Web Processing Services (WPS).  The result?  This initiative makes it possible for these services to be used in the same manner as native ArcGIS geoprocessing tools.  In other words, they appear in the list of tools just as a standard buffer or overlay tool would appear.  Yes, it could be just that easy.

The article explains that “while ArcGIS allows geoprocessing tools to be published as a WPS, [ArcGIS] does not offer a WPS client interface. Consequently, it is not easy to access external non-ArcGIS geoprocessing tools such as simulation models, rich data interfaces, or processing capabilities from any other legacy software that supports the WPS interface.”  This points to the reason why this initiative offers such promise:  “The 52°North Extensible WPS Client for ArcMap was implemented as an open-source extension to ArcGIS that fully integrates into the ArcGIS for Desktop environment. It enables OGC WPS to be accessed and used in the same manner as native ArcGIS geoprocessing tools. This makes it easy to run WPS-based processes and integrate the results of that processing into ArcMap for use with other applications.”

In plain language, because the complex issues grappled with by GIS analysts often require major investments of time to generate models, services, and customized workflows and code, why should each analyst have to create all of this from scratch?  An enormous time savings could be realized if there was an easy way to share these things. This article both explains recent progress in this area but also encourages the community to think creatively about how to pursue further collaborative methods.

52north_initiative

ArcGIS Web Processing Service client architecture.

 

Be a Wise Consumer of “Fun” Posts, too!

January 1, 2017 7 comments

Versions of the following story have made their way around the internet recently:

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.  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 I think as GIS professionals and educators, 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.

international_date_line

The International Date Line (CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=147175).