<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=us-ascii">
<meta name=Generator content="Microsoft Word 12 (filtered medium)">
<style>
<!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;}
@page Section1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.Section1
{page:Section1;}
-->
</style>
<!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang=EN-GB link=blue vlink=purple>
<div class=Section1>
<p class=MsoNormal>Thanks for the interest.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I haven’t tried to collect parish boundaries yet, but
it’s an obvious step forward. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The first thing is to say that I wouldn’t want a load
of effort going into supporting measuring stuff that is better spent mapping
real stuff. So I wouldn’t want to encourage anything that didn’t
have another purpose as well.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Secondly the whole concept of this depends on some
consistency between different areas. Big inconsistencies come from “hinterland”
i.e. a settlement where there is a built-up core, surrounded by an area of low
population. That’s why some of the existing areas produce strange
results. So without trying a bunch of parishes I can’t be certain whether
they would all produce a useful result. On past experience, most will, but some
won’t. Oddly, in some cases guessing at the built-up core from the
population seems to work better than the actual boundary.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So we will need to try this to see what happens. I’m
happy to do that, but not just yet because of real-life pressures, so there is plenty
time to add more parish boundaries before this gets redrawn.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So here are my suggestions.....<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>What the process of analysis needs is a recognisable boundary,
a name to match things up and label things, and a population figure. Everything
else comes from the map database itself. I’ve got some boundaries from
the map, but not yet parishes.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I should get population figures from elsewhere. I think the published
2001 census data goes down to parish level, and although its a bit out of date,
it shouldn’t be a million miles out. I believe there are crown copyright
issues with adding these figures to the map (?) but presumably not when the
processing is off-line.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So on the map we basically need parish boundaries, with a
name.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>For anyone who hasn’t done boundaries before, see
local authority boundaries as a model. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Basically the clearest of these treat each segment of the
boundary as a way tagged “boundary administrative” and “admin_level-x”
where x = 10 for a parish (other numbers for higher admin levels). See <a
href="http://wiki.openstreetmap.org/wiki/Key:admin_level#admin_level">http://wiki.openstreetmap.org/wiki/Key:admin_level#admin_level</a>
<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Then group all the segments with a relation, which is tagged
as boundary, administrative and admin_level 10 with the name of the parish.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>It’s important to do it this way with relations, not
just with ways, because boundaries at different levels overlap each other.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>To process it, I will need the relation to be closed. This
is where many of the local authority boundaries needed a lot of work in the
past. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The best way I know to check closure is with OSM Relation
analyser - <a href="http://betaplace.emaitie.de/webapps.relation-analyzer/">http://betaplace.emaitie.de/webapps.relation-analyzer/</a>
which will tell you whether the boundary is complete (i.e. one joined up line)
and closed (a closed loop). <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Without a closed loop I cannot manipulate the intersections
between roads and boundaries. So “complete” is necessary but insufficient.
<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>And that’s about it.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I need to put this aside for a while because of other things,
but will return to it in a week or two, and try to incorporate any parish
boundaries that are there.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>On the overlapping areas in Medway, I’ll see if increasing
the transparency a bit can improve visibility – it’s not difficult
to adjust, so take another look tomorrow.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>One a slightly different but related subject, with a general
election coming up, does anyone know how things stand with constituency
boundaries?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
</div>
</body>
</html>