1. A method of filtering geographical data, the method comprising: selecting a map region to be retrieved; receiving an identification of a retrieval object and an identification of a retrieval condition; generating a trapezoidal interface whose height represents a threshold value of the identified retrieval condition; identifying, within the selected map region, a target object corresponding to the identified retrieval object and the identified retrieval condition and having a parameter corresponding to the identified retrieval condition whose value is equal or greater value than the threshold value; differentiating, through graphical art, the target object from other objects within a revision of the selected map region; and displaying, with a display device, the revised map region and the trapezoidal interface, wherein the threshold value is a standard value of the retrieval condition to filter the retrieval object and the threshold value is changed depending on the height of the trapezoidal interface, and the revised map region is displayed outside the trapezoidal interface; detecting a revised threshold value of the identified retrieval condition based on a changed height of the trapezoidal interface; identifying, within the selected map region, a revised target object corresponding to the identified retrieval object and the identified retrieval condition and having equal or greater value than the revised threshold value; differentiating, through graphical art, the revised target object from other objects within a subsequent revision of the selected map region; and displaying the subsequent revision of the map region and a modified trapezoidal interface to have the changed height with the display device, wherein the modified trapezoidal interface is modified by adjusting one of a left side, a right side, and an upper side of the trapezoidal interface, by vertically/laterally adjusting both vertices of the upper side of the trapezoidal interface, or by laterally adjusting both vertices of a lower side of the trapezoidal interface.