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What's The Next Thing Up From A Quad?


Wintertime
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I've been Googling some mapping glossaries, but haven't figured this out yet.

 

What do you call the region of a map that consists of four 7.5' quads? For example, if you look here:

 

California Spatial Information Library

 

you'll see the 7.5' quads available for Yosemite Valley and vicinity.

 

I have a printout from the USGS that shows the El Capitan, Half Dome, Wawona, and Mariposa Grove quads as comprising a larger entity that's numbered "437" on the printout. I.e., this is a 15'x15' superquad.

 

Are these just called "15' quads," or is there a special name for them? Also, any idea where those number assignments come from? I haven't been able to find any descriptions of them on the web.

 

Thanks!

Patty

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Hi Patty,

 

A Quadrangle is a four sided Polygon. It can be both Concave or Convex, it can even be a rectangle, but a rectangle cannot be concave or Convex and still be defined as a rectangle, so it is not appropriate to the Mapping world. The Cartographers are flat mapping a convex surface so they use the term Quad or Quadrangle to best describe this, as it will allow for the variables the terrain and shape of the earth will throw at it.

 

A 7.5 minute Quad is displaying 7.5 minutes of Arc, in terms of curvature of Earth. In the Northern Hemisphere this will mean smaller at the top from the bottom, width wise. They should be fairly uniform in length. Appear rectangular, but not really be. A 15 minute Quad would be 4 times bigger than a 7.5. Maybe called a superquad but that is just a marketing term. It is still a quadrangle.

 

It is safest to stick with knowing they are all Quad Maps, and that the Minutes of Arc around the globe such as 7.5, 15, 30, etc will affect the width and height scale of the section of earth you will see. The Minutes of arc simply state the "swath size" of the earth you will see on the particular map scale being offered. The scale will then be representative of the size the paper they chose to print it on.

 

Oh and Patty, here's something you might enjoy:

 

http://www.lib.berkeley.edu/EART/CA/CA_125k/30_minute1.html

 

Some old 30 minute maps worthy of historical comparisons.

 

Rob

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A 15 minute Quad would be 4 times bigger than a 7.5

 

Bigger in the sense it covers 4x more area but the map would be the same size (+/-) and the scale would be smaller. (4x more area on slightly smaller map size as the 7.5') 7.5' is the best scale there is and the USGS standard fo rmost of the USA.

 

I have one or two old 15' mpas of my area.

Edited by Z15
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