Trying to understand getCollectionGraph

$criteria->bindGraph('{"MarketZone":{}}');
$zones = $this->modx->getCollectionGraph('Countries','{"MarketZone":{}}',$criteria);

SELECT `Countries`.`id` AS `Countries_id`, `Countries`.`Country` AS `Countries_Country`, `Countries`.`abbreviation` AS `Countries_abbreviation`, `Countries`.`zone` AS `Countries_zone`, `MarketZone`.`id` AS `MarketZone_id`, `MarketZone`.`zone` AS `MarketZone_zone`, `MarketZone`.`abbreviation` AS `MarketZone_abbreviation` FROM `modx_countries` AS `Countries` LEFT JOIN `modx_market_zone` `MarketZone` ON `Countries`.`zone` = `MarketZone`.`id` WHERE `Countries`.`abbreviation` = 'CA' ORDER BY `Countries`.`id` ASC