Data::Geographics

$ rakupp install Data::Geographics

use Data::Geographics;

my @countries = country-data().keys.sort;
say 'countries : ', @countries.elems;
say '  first three : ', @countries.head(3).join(', ');
say '';
say 'note the shape — country-data($name) is keyed BY the country:';
say '  country-data("Bulgaria")<Bulgaria><Area> = ',
    country-data('Bulgaria')<Bulgaria><Area>;
say '';
say 'city fields : ', city-data('Sofia').head<City Country Latitude Longitude>.grep(*.defined) ?? '' !! '';
my $sofia = city-data('Sofia').head;
say 'one city record:';
for $sofia.keys.sort -> $k {
    next if $k eq 'LocationLink';
    say sprintf('  %-12s %s', $k, $sofia{$k});
}
say '';
say 'only nine countries have city data; the other twenty return an';
say 'empty list, not an error.';

use Data::Geographics;

my ($sofia-lat, $sofia-lon) = 42.69, 23.31;
my ($paris-lat, $paris-lon) = 48.85,  2.35;

say 'geo-distance takes four positionals, two pairs, or one 4-element list:';
say '  metres     : ', geo-distance($sofia-lat, $sofia-lon, $paris-lat, $paris-lon).round;
say '  kilometres : ',
    geo-distance($sofia-lat, $sofia-lon, $paris-lat, $paris-lon, 'kilometers').round;
say '  miles      : ',
    geo-distance($sofia-lat, $sofia-lon, $paris-lat, $paris-lon, 'miles').round;
say '';
sub haversine($la1, $lo1, $la2, $lo2, $R) {
    my ($p1, $p2) = ($la1, $la2).map(* * pi / 180);
    my $dp = ($la2 - $la1) * pi / 180;
    my $dl = ($lo2 - $lo1) * pi / 180;
    my $a = sin($dp/2)**2 + cos($p1) * cos($p2) * sin($dl/2)**2;
    2 * $R * asin(sqrt($a))
}
say 'against a haversine with the EQUATORIAL radius 6378140 m:';
say '  ', haversine($sofia-lat, $sofia-lon, $paris-lat, $paris-lon, 6378140).round;
say 'and with the usual MEAN radius 6371000 m:';
say '  ', haversine($sofia-lat, $sofia-lon, $paris-lat, $paris-lon, 6371000).round;
say '';
say 'the module uses the equatorial radius, so its distances run about';
say '0.11% long against the conventional answer.';
say '';
say 'an unrecognised unit is a clean die:';
my $r = try geo-distance(0, 0, 1, 1, 'furlongs');
say '  units => "furlongs" -> ', $! ?? 'refused' !! $r;

use Data::Geographics;
use Data::Geographics::GeoHash;

my ($lat, $lon) = 42.69, 23.31;
my $gh = geohash($lat, $lon, p => 8);
say 'geohash(42.69, 23.31, :p(8)) = ', $gh;
say '';
my %box = geohash-decode($gh);
say 'decoded box:';
for <latitude longitude> -> $axis {
    say sprintf('  %-10s min=%-14s max=%-14s min <= max ? %s',
                $axis, %box{$axis}<min>, %box{$axis}<max>,
                %box{$axis}<min> <= %box{$axis}<max>);
}
say '';
say 'the magnitudes are right; the labels are not. So the obvious';
say 'containment test reports FALSE for the very point that produced the';
say 'geohash:';
say '  as labelled : ',
    (%box<latitude><min> <= $lat <= %box<latitude><max>);
say '  swapped     : ',
    (%box<latitude><max> <= $lat <= %box<latitude><min>);
say '';
say 'geohash-neighbors is nevertheless CORRECT — it computes from the';
say 'same negative span and the sign cancels:';
say '  ', geohash("sx8df".Str, format => 'neighbors').sort.join(' ');

use Data::Geographics;

my @listed = country-data('fields').list;
my $union = country-data().values.map(*.keys.Slip).unique.elems;
say 'country-data("fields") lists : one country`s keys — 192 or 193,';
say '                               depending on hash order';
say 'the union over all 29 countries : ', $union;
say '';
say 'ingest-country-data sets the list to';
say '  %country-records.values.head.keys.sort';
say '— the keys of whichever country hash iteration puts first. So real';
say 'data is unreachable through the $fields argument, and the COUNT';
say 'differs between engines because hash order does.';
say '';
my @missing = country-data().values.map(*.keys.Slip).unique.grep({ $_ !~~ any(@listed) }).sort;
say 'fields present in the data and absent from the whitelist : ',
    @missing >= 10 ?? 'ten or more' !! @missing.elems;
say '  they include BorderingCountries, ExportPartners, ImportPartners,';
say '  NaturalHazards and InfectiousDiseases.';
say '';
say 'ask for a country and read the hash; do not filter by field.';

use Data::Geographics;

say 'the shapes that behave identically on both engines:';
say '  country-data($name)<$name><Field>';
say '  city-data($city) / city-data([$country, Whatever, Whatever])';
say '  geo-distance(…) in any of its argument forms';
say '  geohash($lat, $lon, :p($n))  and  geohash($gh, format => "neighbors")';
say '';
say 'a bare Str spec to city-data searches the CITY column only:';
say '  city-data("Bulgaria").elems          : ', city-data('Bulgaria').elems;
say '  city-data(["Bulgaria", *, *]).elems  : ',
    city-data(['Bulgaria', Whatever, Whatever]).elems;
say '';
say 'and city-data(Whatever) dies even though city-data() with no';
say 'arguments returns everything.';
say '';
say 'one last thing worth knowing before you deploy: META declares';
say '"depends": [] while the module does `use JSON::Fast`. It can install';
say 'into a store where it will not load.';