Mapping Hacks

Set Up an OpenGuide for Your Hometown #97

Chapter 9, Mapping with Other People

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HACK

my $rdf = get('http://london.openguides.org/index.

cgi?action=index&format=rdf');

$rdf =~ tr/\240/\040/; # XML-toxic characters

my @triples = $parser->parse_rdf($rdf);

# find all triples where the subject is of rdf:type geo:SpatialThing

my @spaces = grep {$_->[2] =~ /SpatialThing/} @triples;

my @points; # an empty list to hold our points

foreach my $s (@spaces) {

my $url = $s->[0]; # get the subject url of the triple

warn("reading $url");

my @t = $parser->parse_uri($url);

my ($lat) = grep {$_->[1] =~ /wgs84_pos\#lat/} @t;

next unless $lat; # don't bother if we can't find a latitude

next if $lat =~ m/0d/ or $lat !~ m/51/; # we know these are wrong

my ($lon) = grep {$_->[1] =~ /wgs84_pos\#long/} @t;

if ($lat =~ m/\d+d \d+m/) {

# this point is in DMS, not decimal, format

foreach ($lat,$lon) {

my ($direction,$d,$m,$s) = $_ =~ /(-?)([\d]+)d (\d+)m ([\d\.]+)s/;

$_ = $d + $m/60 + $s/3600;

$_ = 0-$_ if $direction;

}

}

push @points, { lat => $lat, long => $lon, url => $url};

}

Plotting Places over Open Space

Now that we have a list of points, we’re ready to roll! What we can do with

them, though, depends on where in the world we are. In London, bereft of

copyright-free, public domain base maps, the first visualization of Open-

Guides was just a plot of points on a blank white background.

The

SVG::Plot module, available ...