using php to build map grid string -

i'm using pp3diso build game map. library uses string determine image use in each grid cell this: 01,01,01,01,01,01,01:02,01,01,01,01,01,01:01,01,01,01,01,01,01:01,01,01,01,01,01,01:01,01,01,01,01,01,01:01,01,01,01,01,01,01. i'm trying piece type of string in php while loops, code seems stop after first iteration (01,01,01,01,01,01,01,01:). how can code below create full string?

$mapstr = '';  $x = 1; $y = 1;  while($x <= 500){     while($y <= 500){         $sql = 'select * '.cities.' city_x = '.$x.' , city_y = '.$y;         $result = $db->sql_query($sql);         $city = $db->sql_fetchrow($result);          if($city){             $mapstr .= '02'.(($x < 500) ? ',' : '');         }else{             $mapstr .= '01'.(($x < 500) ? ',' : '');         }          $y++;     }      if($x == 500){         $mapstr .= ':';     }else if($x == 500 && $y == 500){         $mapstr .= '';     }      $x++; }  $return['map'] = $mapstr; 

also, there more efficient way of doing instead of querying database each cell?

turned out easier in for loop:

$columns = 501; $rows = 501;  for($x = 1; $x < $columns; $x++){     for($y = 1; $y < $rows; $y++){         $sql = 'select * '.cities.' city_x = '.$x.' , city_y = '.$y;         $result = $db->sql_query($sql);         $city = $db->sql_fetchrow($result);          if($city){             $mapstr .= '02';         }else{             $mapstr .= '01';         }          if($y < 500){             $mapstr .= ',';         }elseif($y == 500){             $mapstr .= ':<br />';         }     }      $sql = 'select * '.cities.' city_x = '.$x.' , city_y = '.$y;     $result = $db->sql_query($sql);     $city = $db->sql_fetchrow($result);      if($city){         $mapstr .= '02';     }else{         $mapstr .= '01';     }      if($y < 500){         $mapstr .= ',';     }elseif($y == 500){         $mapstr .= ':<br />';     } } echo $mapstr;