[Abagail]

The best way (the way I'd recommend, atleast) is using dynamic areas provided by the Streamer Plugin.

Area natives:

pawn Код:

native STREAMER_TAG_AREA CreateDynamicCircle(Float:x, Float:y, Float:size, worldid = -1, interiorid = -1, playerid = -1);
native STREAMER_TAG_AREA CreateDynamicCylinder(Float:x, Float:y, Float:minz, Float:maxz, Float:size, worldid = -1, interiorid = -1, playerid = -1);
native STREAMER_TAG_AREA CreateDynamicSphere(Float:x, Float:y, Float:z, Float:size, worldid = -1, interiorid = -1, playerid = -1);
native STREAMER_TAG_AREA CreateDynamicRectangle(Float:minx, Float:miny, Float:maxx, Float:maxy, worldid = -1, interiorid = -1, playerid = -1);
native STREAMER_TAG_AREA CreateDynamicCuboid(Float:minx, Float:miny, Float:minz, Float:maxx, Float:maxy, Float:maxz, worldid = -1, interiorid = -1, playerid = -1);
native STREAMER_TAG_AREA CreateDynamicCube(Float:minx, Float:miny, Float:minz, Float:maxx, Float:maxy, Float:maxz, worldid = -1, interiorid = -1, playerid = -1);
native STREAMER_TAG_AREA CreateDynamicPolygon(Float:points[], Float:minz = -FLOAT_INFINITY, Float:maxz = FLOAT_INFINITY, maxpoints = sizeof points, worldid = -1, interiorid = -1, playerid = -1);
native DestroyDynamicArea(STREAMER_TAG_AREA areaid);
native IsValidDynamicArea(STREAMER_TAG_AREA areaid);
native GetDynamicPolygonPoints(STREAMER_TAG_AREA areaid, Float:points[], maxpoints = sizeof points);
native GetDynamicPolygonNumberPoints(STREAMER_TAG_AREA areaid);
native TogglePlayerDynamicArea(playerid, STREAMER_TAG_AREA areaid, toggle);
native TogglePlayerAllDynamicAreas(playerid, toggle);
native IsPlayerInDynamicArea(playerid, STREAMER_TAG_AREA areaid, recheck = 0);
native IsPlayerInAnyDynamicArea(playerid, recheck = 0);
native IsAnyPlayerInDynamicArea(STREAMER_TAG_AREA areaid, recheck = 0);
native IsAnyPlayerInAnyDynamicArea(recheck = 0);
native GetPlayerDynamicAreas(playerid, STREAMER_TAG_AREA areas[], maxareas = sizeof areas);
native GetPlayerNumberDynamicAreas(playerid);
native IsPointInDynamicArea(STREAMER_TAG_AREA areaid, Float:x, Float:y, Float:z);
native IsPointInAnyDynamicArea(Float:x, Float:y, Float:z);
native GetDynamicAreasForPoint(Float:x, Float:y, Float:z, STREAMER_TAG_AREA areas[], maxareas = sizeof areas);
native GetNumberDynamicAreasForPoint(Float:x, Float:y, Float:z);
native AttachDynamicAreaToObject(STREAMER_TAG_AREA areaid, STREAMER_TAG_OBJECT_ALT objectid, type = STREAMER_OBJECT_TYPE_DYNAMIC, playerid = INVALID_PLAYER_ID, Float:offsetx = 0.0, Float:offsety = 0.0, Float:offsetz = 0.0);
native AttachDynamicAreaToPlayer(STREAMER_TAG_AREA areaid, playerid, Float:offsetx = 0.0, Float:offsety = 0.0, Float:offsetz = 0.0);
native AttachDynamicAreaToVehicle(STREAMER_TAG_AREA areaid, vehicleid, Float:offsetx = 0.0, Float:offsety = 0.0, Float:offsetz = 0.0);

In this case, a rectangle would probably be the best to do the job. To detect when the player enters the area, the OnPlayerEnterDynamicArea callback is called.