jgg     2014 34 (2):  165-168    ISSN: 0412-1961  CN: 21-1139/TG STUDY ON RELATION OF RESIDUAL DISTRIBUTION TO GEOGRAPHIC  LOCATION OF GPS SITES Xi’an Division of Surveying and Mapping，Xi’an 710054 Received: 2013-07-07  Revised: null  Online: 2014-04-21 Supporting info