public function importJson($jsonData)
    {
        $json = json_decode($jsonData, true);

        if ($json === null) {
            throw new \InvalidArgumentException("Footprint json is not a valid");
        }

        if (!is_array($json)) {
            throw new \InvalidArgumentException("Footprint json data is not a valid");
        }

        $this->_data += $json;
    }