Weather API not support for some WOIED ?

Hi,
 I am using yahoo weather api for iphone application. What I am doing is, tracking user's current location and then get the WOEID. Then I request weather info for that WOEID (http://weather.yahooapis.com/forecastjson?w=2189675)

But weather API support for only few WOEID of local cities, others give "null" ... How can I solve this problem. Is there a way to get the WOEID of the main cities which are supported weather API?

Please give me a help. Thanks in advanced