Observations from Mexico

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Chris Smith
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Observations from Mexico

Post by Chris Smith » December 21st, 2014, 10:56 am

HerpMapper map for observations reported from ‪Mexico

http://www.herpmapper.org
Image

Flyer in Spanish: http://www.herpmapper.org/content/pdf/h ... yer-es.pdf

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justinm
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Re: Observations from Mexico

Post by justinm » December 22nd, 2014, 7:07 am

Wow this is super cool! I can't wait to add some data to Mexico someday.

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jonathan
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Re: Observations from Mexico

Post by jonathan » December 25th, 2014, 10:28 pm

Hexagons! I like hexagons!

If I undestand the map correctly, the hexagons are only used for large counties (or whatever they call them there?)

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Don Becker
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Re: Observations from Mexico

Post by Don Becker » December 28th, 2014, 5:12 am

They are used in place of counties.

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Chris Smith
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Re: Observations from Mexico

Post by Chris Smith » December 30th, 2014, 7:23 pm

These hexagons are just another way to visualize these data. They are sufficiently large to protect sensitive species, but mix it up a bit from looking at counties. Just experimenting with ways to visualize data, and spark interest in filling gaps.

-Chris

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Don Becker
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Re: Observations from Mexico

Post by Don Becker » December 31st, 2014, 7:59 am

I have been experimenting with them in place of counties because 1. Some counties are very small, and 2. They are much faster to render than counties.

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Re: Observations from Mexico

Post by chris_mcmartin » December 31st, 2014, 9:19 am

How hard is it to modify the size of the hexagons? I could see value in making them smaller (for a more refined look), but not TOO small (compromising localities etc.).

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jonathan
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Re: Observations from Mexico

Post by jonathan » December 31st, 2014, 7:40 pm

Can you explain how the hexagons work? It appears that some of them are sized to fit inside counties. Are they rounded off to various approximate sizes?

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chris_mcmartin
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Re: Observations from Mexico

Post by chris_mcmartin » December 31st, 2014, 7:47 pm

If I understand the concept correctly, it's an arbitrarily-sized/shaped area, in which the observation is located SOMEWHERE (though not necessarily the center). They're all equal size, but when the hexagon is "randomized" such that part of the hexagon is over the ocean, it doesn't show up. That detracts somewhat from the obscuration of the observation in some instances, since you can see from the example given that sometimes a very small portion of the hexagon is actually on land, thus helping a viewer narrow down the likely location of an observation. That being said, it's not much different than an observation found in a very small county narrowing down the location more so than one found in a very large county, if counties are what's used to populate the map.

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Don Becker
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Re: Observations from Mexico

Post by Don Becker » January 1st, 2015, 10:05 am

http://www.psychoticnature.com/files/misc/grid.png

I am not embedding that image since it is 6000x3585. If you view it though, you can see the entire grid drawn out. Picture those hex tiles the same as counties. If the point falls anywhere inside of it, it gets filled in. Tile 0,0 is centered on Lat/Lon of 0,0 as well, and the tiles spread from there. The grid system is based on a Spherical Mercator Projection. The size of tiles can be changed very easily, and no matter the size, Tile 0,0 is always centered on Lat/Lon 0,0 still.

The primary issue with this method are in locations where a hexagon only covers a very small piece of land. If a record is from that small area, it will color the hexagon, but you can tell that only part of the hexagon includes land, and is not in the Ocean. Another example may be that if a species is only known from East of the Mississippi River, and the hexagon it is in falls mostly on the West side, with only a small corner or sliver drawn onto the East side. Chris and I have been screen the few maps we have put up to watch for those issues thus far though, and it is the primary reason this type of map is not more widely used on HerpMapper right now.

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Don Becker
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Re: Observations from Mexico

Post by Don Becker » January 1st, 2015, 10:12 am

Btw, in case someone doesn't remember my past posts about hexagon maps. The EPA EMAP program using a grid of hexagonal tiles as well, and is originally where I got the idea. The difference is that they actually divide the spherical earth into hexagons, which look fine when projected into most UTM maps for places in the US, but look really skewed when projected with Spherical Mercator, which is often called Web Mercator because it is used for most web based mapping projects. I use Spherical Mercator for easy of rendering and compatibility with other map systems if we decide to make a google maps interface or something, so it made more sense to make a mercator based grid. In the areas where the hexagons would represent the smallest areas in the far North and far South, herps don't tend to exist.

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Don Becker
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Re: Observations from Mexico

Post by Don Becker » January 1st, 2015, 10:14 am

Here is an example of a map using the EMAP grid.

Image

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Don Becker
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Re: Observations from Mexico

Post by Don Becker » January 1st, 2015, 10:20 am

AH HA! Found the other page I was looking for

http://www.epa.gov/nheerl/arm/global_grids.htm

And I believe this software can be used to generate grids if you want to put them on a spherical globe

http://webpages.sou.edu/~sahrk/dgg/dggrid/dggrid.html

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