Filter Results Inside a Polygon

In this tutorial, you’ll learn how to filter results around a polygonal location. This location can either be set manually or taken from the current user position.

Dataset

The dataset contains 3000+ of the biggest airports in the world.

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[
 {
    "objectID": "3797",
    "name": "John F Kennedy Intl",
    "city": "New York",
    "country": "United States",
    "iata_code": "JFK",
    "_geoloc": {
      "lat": 40.639751,
      "lng": -73.778925
    },
    "links_count": 911
  }
]

To tell Algolia where each record is located, we need to have the latitude and longitude stored in the _geoloc attribute.

You can download the dataset here. Have look at how to import it in Algolia here

Initialize the client

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// composer autoload
require __DIR__ . '/vendor/autoload.php';

// if you are not using composer
// require_once 'path/to/algoliasearch.php';

$client = \Algolia\AlgoliaSearch\SearchClient::create(
  'YourApplicationID',
  'YourAdminAPIKey'
);

$index = $client->initIndex('your_index_name');

Configure Index Settings

Even if we want to sort by distance to a location, we need the textual relevance to be good in case we refine the search with a query.

For that let’s configure the index.

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$index->setSettings({
  'searchableAttributes' => [
    'name',
    'city',
    'country',
    'iata_code'
  ],
  'customRanking': [
    'desc(links_count)'
  ]
});

Searchable attributes

We’re going to search in our 4 textual attributes: name, city, country and iata_code.

Custom Ranking

We will use the number of other connected airports to any airport as a ranking metric - the more connection the better.

Filtering inside a polygonal area

Let’s filter inside the United State of America.

USA can be considered as a polygon:

To filter inside this polygon we need the latitude and longitude of all the points:

  • 42.01,-124.31,
  • 48.835509470063045,-124.40453125000005
  • 45.01082951668149,-65.95726562500005
  • 31.247243545293433,-81.06578125000004
  • 25.924152577235226,-97.68234374999997
  • 32.300311895879545,-117.54828125

We are going to use the insidePolygon parameter:

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$polygon = [
  42.01,
  -124.31,

  48.835509470063045,
  -124.40453125000005,

  45.01082951668149,
  -65.95726562500005,

  31.247243545293433,
  -81.06578125000004,

  25.924152577235226,
  -97.68234374999997,

  32.300311895879545,
  -117.54828125
];

$results = $index->search('', [
  'insidePolygon' => [$polygon]
]);

We are using the empty query ('') because we want all airports.

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