The transition of chicagocrime.org has been noted by geo-bloggers, but they
are missing a key part of the story: the resources that had been hosted on
chicagocrime.org are not dead at all. They have been moved to a new host.
Their original URLs have been retired, but the resources themselves carry on.
I'm not speaking figuratively. Stability is a virtue, but Web architecture
makes it possible for resources to move when necessary. The chicagocrime.org
move is a perfectly ordinary transition of resources on the Web.
How is this accomplished? Requests for http://chicagocrime.org are redirected
to http://everyblock.com. I don't mean that you get a web page that says,
"click here to go to the new web site". I don't mean that
http://chicagocrime.org is maintained as a proxy server for content from
http://everyblock.com. I mean that the Chicago Crime host responds to your
request with a 301 Moved Permanently response:
sean@lenny:~$ curl -v http://chicagocrime.org/
* About to connect() to chicagocrime.org port 80
* Trying 64.207.128.91... connected
* Connected to chicagocrime.org (64.207.128.91) port 80
> GET / HTTP/1.1
> Host: chicagocrime.org
> Accept: */*
>
< HTTP/1.1 301 Moved Permanently
< Server: nginx/0.5.35
< Date: Tue, 05 Feb 2008 16:57:32 GMT
< Content-Type: text/html
< Content-Length: 185
< Connection: keep-alive
< Location: http://chicago.everyblock.com/crime/
<html>
<head><title>301 Moved Permanently</title></head>
<body bgcolor="white">
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx/0.5.35</center>
</body>
</html>
* Connection #0 to host chicagocrime.org left intact
* Closing connection #0
That response tells user agents that the resource formerly found at
http://chicagocrime.org/ has been moved to
http://chicago.everyblock.com/crime/, and that user agents may consider it to
be the same resource. Its representation ("format" to you GIS folks) may have
changed a little bit, and the less the better for non-human users, but it
should be substantially the same. Somewhat smart user agents, like your web
browser, will follow up on this response with a request to the new resource
location, making the redirect more or less invisible to you. Smarter user
agents might update their bookmarks accordingly.
Look a little more deeply and you'll notice that not only has the root resource been permanently moved, the descendent resources have been moved as well:
sean@lenny:~$ curl -v http://www.chicagocrime.org/zipcodes/60615/
* About to connect() to www.chicagocrime.org port 80
* Trying 64.207.128.91... connected
* Connected to www.chicagocrime.org (64.207.128.91) port 80
> GET /zipcodes/60615/ HTTP/1.1
> Host: www.chicagocrime.org
> Accept: */*
>
< HTTP/1.1 301 Moved Permanently
< Server: nginx/0.5.35
< Date: Tue, 05 Feb 2008 17:11:30 GMT
< Content-Type: text/html
< Content-Length: 185
< Connection: keep-alive
< Location: http://chicago.everyblock.com/locations/zipcodes/60615/
<html>
<head><title>301 Moved Permanently</title></head>
<body bgcolor="white">
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx/0.5.35</center>
</body>
</html>
* Connection #0 to host www.chicagocrime.org left intact
* Closing connection #0
Browse to http://www.chicagocrime.org/zipcodes/60615/ to see this in action.
Starting with a sane URL scheme as Chicago Crime did certainly makes the
transition a lot easier.
I can't say for sure that every single resource from chicagocrime.org has been
moved in this way, but it wouldn't surprise me if they have, and if it took no
more than 20 lines of configuration on the old server. By the way, HTTP
specifies a status code that can be used to tell user agents that a resource
really is no more: 410 Gone. I wouldn't be surprised if that was employed
somewhere on what's left of chicagocrime.org.
Chicago Crime resources
are moved, the Web as an application goes on without missing a beat. At least
the pieces of it that were only loosely coupled to http://chicagocrime.org; any
script that was downloading resources from the old site without following
redirection is well and surely (and perhaps rightly) broken. Geographic sites
and services can migrate or evolve using the same mechanism, a mechanism that
is built into the Web. Does your GIS "web" service client understand
redirects, or is it crazy-glued to those service endpoints?
All of the above is elementary web knowledge, but the Chicago Crime move is a
nice lesson in applying resource-oriented thinking to a "GeoWeb" site.