JSON encoding from wordpress database values

I need a proper JSON file with “geo_langitude”, “geo_latitude”, “adress” & “url” values

I have wp database with post_meta “property” – “geo_langitude” “geo_latitude” & “address” in there.
my file is smth like that

    <?php   
    function return_markers($count) {
        $query = new WP_Query('post_type=property&posts_per_page=-1&orderby=menu_order&order=DESC&post_status=publish');
        $array = array();
        $i = 0;

    for ($i = 0; $i< $count; $i++) {
      $elem = array(
        't' => 'string '.$i,
        'x' => get_post_meta($post->ID,'geo_latitude',true),
        'y' => get_post_meta($post->ID,'geo_longitude',true),
        'z' => $i
      );
      $array[] = $elem;
    }
    echo json_encode($elem);
  };

  return_markers($i);
?>

It’s my first time using JSON so I have troubles and I don’t know where. =(

with random markers work perfectly:

    <?php
  function return_markers($count) {
    $array = array ();
    for ($i = 0; $i< $count; $i++) {
      $elem = array(
        't' => 'string '.$i,
        'x' => 23 + (rand ( 0 , 10000 ) / 10000) * 5,
        'y' => 56.2 + (rand ( 0 , 10000 ) / 10000) * 0.8,
        'url' => '#map_redirect_'.$i,
        'z' => $i
      );
      $array[] = $elem;
    }
    echo json_encode($array);
  };

  return_markers(23);
?>