从China_City.txt文件中读取前5个城市的经纬度坐标，按上下左右各增加1度，得到最东、最西的经度和最北、最南的纬度，作为相应城市的范围。-Read the China_City.txt file of the latitude and longitude coordinates of the first 5cities,add 1 degrees to each directions as the extent of each city.