<p>A "God's view" map of Milky Way as seen from far Galactic North (in Coma Berenices). The star-like lines center in a yellow dot representing the position of Sun. The spokes of that "star" are marked with constellation abbreviations, "Cas" for "Cassiopeia", etc. The spiral arms are colored differently in order to highlight what structure belongs to which arm. H II regions are marked as dots colored in the same color as their spiral arm. They come in three sizes, measured by the <i>excitation parameter</i> U: 
</p>
<ol><li>small - U &gt; 200 pc cm<sup>-2</sup></li>
<li>medium - 200 &gt; U &gt; 110 pc cm<sup>-2</sup></li>
<li>large - 110 &gt; U &gt; 70 pc cm<sup>-2</sup></li></ol>
<a href="//commons.wikimedia.org/wiki/User:Rursus" title="User:Rursus">User:Rursus</a>
CC BY-SA 3.0
<p>A redevelopment of <a href="//commons.wikimedia.org/wiki/File:Milky_Way_Arms-Hypothetical.png" title="File:Milky Way Arms-Hypothetical.png">Image:Milky Way Arms-Hypothetical.png</a>: details about <b>method</b> below.<br></p>
<a href="//commons.wikimedia.org/wiki/User:YUL89YYZ" title="User:YUL89YYZ">User:YUL89YYZ</a>, <a href="//commons.wikimedia.org/w/index.php?title=User:Ctachme&amp;action=edit&amp;redlink=1" class="new" title="User:Ctachme (page does not exist)">User:Ctachme</a>, Kevin Krisciunas, Bill Yenne: "The Pictorial Atlas of the Universe", page 145 (<a href="//commons.wikimedia.org/wiki/Special:BookSources/1-85422-025-X" title="Special:BookSources/1-85422-025-X">ISBN 1-85422-025-X</a>) and µOR.