Update (2008-03-31)
A related post.
Update (2008-03-18)
I've created 2 mock feeds, one using Andrew's multiple location proposal: http://sgillies.net/files/multi-location.atom, and one using multiple entries: http://sgillies.net/files/multi-entry.atom. Add each to your reader of choice. I believe the second, with 3 entries, comes through geographically "dumb" readers in much better shape. In other words: it degrades gracefully. There is more discussion of this in the comments.
Andrew Turner has 2 new GeoRSS proposals: External geometry includes an idea I posted to Geo-Web-REST after reading Benjamin Carlyle's XML Semantic Web proposal, and Multiple locations tries to address entries that have several related locations.
I'm having an immediate negative reaction to the multiple locations proposal. It looks to me like a proposal to extend RSS by embedding items (or entries) within items, something that could have unpredictable consequences for syndication architectures. Instead, I recommend rolling with syndication architecture as it is. Feed entries are cheap: if you need more locations, add more entries. Here's my multiple entry take on Andrew's proposed single entry (omitting the external location):
<feed
xmlns="http://www.w3.org/2005/Atom"
xmlns:georss="http://www.georss.org/georss"
xmlns:gml="http://www.opengis.net/gml"
>
<entry>
<id>urn:uuid:7e8ee974-9181-4eae-ad65-55d29175d942</id>
<link href="http://example.org/entries/1"/>
<title>Cedarburg Trip</title>
<summary>We went to visit downtown Cedarburg before the
conference. Had some great sandwiches at Joe's. If you
haven't been to Cedarburg, Wisconsin, then you haven't
really experienced the MidWest...</summary>
<content type="html" src="http://example.org/entries/1"/>
</entry>
<entry>
<id>urn:uuid:53664db3-4598-45d4-a727-022c6203322e</id>
<link rel="related" href="http://example.org/entries/1"/>
<title>Downtown Cedarburg, Wis.</title>
<summary>Went to visit downtown Cedarburg...</summary>
<georss:where>
<gml:Point>
<gml:pos>43.296700 -87.98750</gml:pos>
</gml:Point>
</georss:where>
</entry>
<entry>
<id>urn:uuid:2528d1b4-b5a9-415c-be69-f83974e3e6af</id>
<link rel="related" href="http://example.org/entries/1"/>
<title>Convention Center</title>
<georss:where>
<gml:LineString>
<gml:posList>43.296700 -87.987500 43.3 -88 -44 -89</gml:posList>
</gml:LineString>
</georss:where>
</entry>
</feed>
(Yes, I used to recommend the GeoRSS "Simple" encoding, but now I use and endorse only the GML encoding.)
Early GeoRSS discussions were not so much about syndicating GIS data as they were about "geo-tagging" feeds and feed entries. Geographic annotation, in other words. There's no need to invent new mechanisms for annotation because syndication architecture already has one: commentary. People (hopefully) will leave comments via this blog post that correct my mistakes, offer different interpretations, ask for clarification, tell me that GML already does all this, or remind me about Manifold's incredible value. I don't think geographic commentary – "by the way, downtown Cedarburg is at (43.296700,-87.98750)", and "furthermore, the Convention Center is demarcated by the line (43.296700,-87.987500,43.3,-88,-44,-89)" – is a different category. If I were in the business of parsing and geocoding locations from documents and syndicating the results, I'd have my code engage the document as if it were a blog post and drop a geo-referenced comment for each location.
There is even a formal document about comment entries: RFC 4685, the Atom Threading Extension. Its in-reply-to element could be used in the feed above (highlighted with a little extra whitespace) to clarify the relationship between content and annotation entries:
<feed
xmlns="http://www.w3.org/2005/Atom"
xmlns:georss="http://www.georss.org/georss"
xmlns:gml="http://www.opengis.net/gml"
xmlns:thr="http://purl.org/syndication/thread/1.0"
>
<entry>
<id>urn:uuid:7e8ee974-9181-4eae-ad65-55d29175d942</id>
<link href="http://example.org/entries/1"/>
<title>Cedarburg Trip</title>
<summary>We went to visit downtown Cedarburg before the
conference. Had some great sandwiches at Joe's. If you
haven't been to Cedarburg, Wisconsin, then you haven't
really experienced the MidWest...</summary>
<content type="application/xhtml+xml" src="http://example.org/entries/1"/>
</entry>
<entry>
<id>urn:uuid:53664db3-4598-45d4-a727-022c6203322e</id>
<link rel="related" href="http://example.org/entries/1"/>
<thr:in-reply-to
ref="urn:uuid:7e8ee974-9181-4eae-ad65-55d29175d942"
type="application/xhtml+xml"
href="http://www.example.org/entries/1"
/>
<title>Downtown Cedarburg, Wis.</title>
<summary>Went to visit downtown Cedarburg...</summary>
<georss:where>
<gml:Point>
<gml:pos>43.296700 -87.98750</gml:pos>
</gml:Point>
</georss:where>
</entry>
<entry>
<id>urn:uuid:2528d1b4-b5a9-415c-be69-f83974e3e6af</id>
<link rel="related" href="http://example.org/entries/1"/>
<thr:in-reply-to
ref="urn:uuid:7e8ee974-9181-4eae-ad65-55d29175d942"
type="application/xhtml+xml"
href="http://www.example.org/entries/1"
/>
<title>Convention Center</title>
<georss:where>
<gml:LineString>
<gml:posList>43.296700 -87.987500 43.3 -88 -44, -89</gml:posList>
</gml:LineString>
</georss:where>
</entry>
</feed>
RFC 4685's in-reply-to might even be useful outside of Atom.
Multiple locations represented as multiple entries is something that works (even if non-geographically) in our news readers right now. A good enough reader will find the geographic annotations in my examples, even if they are not completely understood, and see that they are related to the first entry.
