Using dynamic variables in URL
It looks like you need to know how to create a string that contains:
steetalert.co.zw/write_data.php?Longitude=12.124311,Latitude=27,766785

Its quite easy (I think) try this:

const int cDecimalPlaces(6);
String szLon = String(fLongitude, cDecimalPlaces);
String szLat = String(fLatitude, cDecimalPlaces);
String szUrl = "steetalert.co.zw/write_data.php?Longitude=" + szLon ",Latitude=" + szLat;


Normally I would use sprint or a Format function, but I can't find those in the reference.