The above map shows some of my completed island mapping projects. Each icon contains the name of the primary island associated with the project and a link to the post. Once all of my projects are posted, the map will be covered with icons. To productively use the map, zoom into a region of interest. Then select an icon.

Each of my maps is constructed of numerous layers of information. All of the layers are vector files. I will make these files available upon request. You are free to use them with certain restrictions - 1) Don't sell them. You can use them on research projects, post them to your website or things of that nature. If you aren't sure about the use of my maps, drop me a line and we can discuss your idea. 2) Give me credit when you use my vectors or images of my maps. Credit them to Peter Minton @ EVS-Islands

If I have the island vector file(s) and based upon your need, I will make them available. Images of my maps are yours to download and use, with the above restrictions applicable. Enjoy!

Comparison - NGA PGS to EVS Precision Vectors

Comparison - NGA PGS to EVS Precision Vectors (1-6,250)

Comparison - NGA PGS to EVS Precision Vectors (1:6,250)

I know a good deal about global shoreline vector files. Specifically, global shoreline vector files that are free, available to the public and relatively easy to load and work with. This post's focus is a comparison of NGA's Prototype Global Shoreline (PGS) to Enhanced Vector Shoreline (EVS) Precision shorelines. This is not my first comparison of these two shorelines and it probably won't be my last, but here it goes.

NGA PGS vectors too often wobble off of the imaged coastline unnecessarily. The NGA PGS vectors were derived from Landsat ETM+ imagery, the same imagery I use to create EVS Precision shorelines. The above image is a small portion of Somalia's shoreline. The Landsat image is cloud free and the shoreline is easily distinguishable. NGA PGS used a complicated formula to determine the shoreline, but I don't see why their vectors misplot by as much as 41 meters from the imaged shoreline. No, this doesn't happen all of the time, but it happens enough, that if I am working at very large scales (1:50,000 to 1:12,500), I must redo the shoreline. Their shoreline is too far from image shoreline true.

I've been doing EVS Precision mapping for over 9 going on 10 years and my opinion concerning NGA PGS has not changed. Don't get me wrong, NGA PGS is the most detailed global shoreline available, one that I recommend heartily. However, for my work, creating detailed island maps, it isn't good enough.

Enjoy!

Labels: , ,

Posted by Mr Minton on Sunday, April 19, 2009 at 4/19/2009 07:11:00 PM |

That's some assumption you are making there. How do you know the imagery you are using are made when the sea level was at, well... sea level? Or that it was rectified based on a sufficiently correct terrain model?
I don't think you can base any kind of accuracy measurement from data that comes from monoplotting. Especially considering the type of data you are using.

Posted by Anonymous Anonymous | 4/19/2009 09:35:00 PM  

Anon,

Thanks for your observations. In rereading the NGA PGS Whitepaper (at their website), their vectors approximate the High Water Line. Further into their explanation, they intend their shorelines to be used at scales 1:75,000 and smaller. They admit that the accuracy of shoreline derived from Short-Wave Infra-Red bands is 50-meters (RMS). Another admission "Because the shoreline was primarily computer generated, it is not the smooth line you find on charts and it also contains many short segments." I believe this ever-improving vector defined shoreline is the best global shoreline available. However, I would rather digitize my island shorelines instead of using the rough NGA PGS shorelines.

At the scales my maps are viewed and used (typically between 1:100,000 to 1:25,000) and considering the resolution limitations of Landsat ETM+ (14.5 Meters per pixel), my monoplotted maps provide a reasonably accurate picture of the islands I have digitized using Landsat ETM+ as my base imagery.

How's life at ESRI?

Posted by Blogger Mr Minton | 4/19/2009 10:40:00 PM  

Can you provide downloads to vector versions of your images, specifically see http://en.wikipedia.org/wiki/Wikipedia:GL/MAP#Pitcairn_Islands

Posted by Anonymous Anonymous | 5/03/2009 12:19:00 PM  

Post a Comment

Links to this post

Create a Link

3 Comments:

That's some assumption you are making there. How do you know the imagery you are using are made when the sea level was at, well... sea level? Or that it was rectified based on a sufficiently correct terrain model?
I don't think you can base any kind of accuracy measurement from data that comes from monoplotting. Especially considering the type of data you are using.

By Anonymous Anonymous, at 4/19/2009 09:35:00 PM  

Anon,

Thanks for your observations. In rereading the NGA PGS Whitepaper (at their website), their vectors approximate the High Water Line. Further into their explanation, they intend their shorelines to be used at scales 1:75,000 and smaller. They admit that the accuracy of shoreline derived from Short-Wave Infra-Red bands is 50-meters (RMS). Another admission "Because the shoreline was primarily computer generated, it is not the smooth line you find on charts and it also contains many short segments." I believe this ever-improving vector defined shoreline is the best global shoreline available. However, I would rather digitize my island shorelines instead of using the rough NGA PGS shorelines.

At the scales my maps are viewed and used (typically between 1:100,000 to 1:25,000) and considering the resolution limitations of Landsat ETM+ (14.5 Meters per pixel), my monoplotted maps provide a reasonably accurate picture of the islands I have digitized using Landsat ETM+ as my base imagery.

How's life at ESRI?

By Blogger Mr Minton, at 4/19/2009 10:40:00 PM  

Can you provide downloads to vector versions of your images, specifically see http://en.wikipedia.org/wiki/Wikipedia:GL/MAP#Pitcairn_Islands

By Anonymous Anonymous, at 5/03/2009 12:19:00 PM  

Post a Comment

Powered by Blogger

E-mail Me

If You Enjoy My Maps,
Make A Donation


  • Google PageRank Checker - Page Rank Calculator

    About me

    • I'm Mr Minton
    • From San Diego, CA
    My profile

    Calendar


    Get your own calendar

    Software I Recommend

    Purchase Global Mapper v9

    Trial Download Global Mapper v9

    A moderately priced, easy-to-use GIS package, which I use to load, view and work with Landsat ETM+ imagery from which I digitize layers of information for my island maps.

    EVS Islands Projects

    EVS Islands RSS Feeds

    Subscribe to
    Posts [Atom]


    Google Reader or Homepage
    del.icio.us EVS-Islands
    Add to My Yahoo!
    Subscribe with Bloglines
    Subscribe in NewsGator Online
    myFeedster
    Add to My AOL
    Subscribe in Rojo

    Learn how to make RSS Feed Buttons

    Search


    Previous posts

    Archives

    Links

  • WVS Coastlines
  • Landsat-2000 ETM
  • Global Mapper
  • MARPLOT Mapping Program
  • NGA Prototype Global Shoreline
  • GEONet Names
  • NASA Earth



    • Creative Commons License

    This work is licensed under a Creative Commons Attribution 2.5 License
    .

    Locations of visitors to this page