tailieunhanh - Beginning Google Maps Applications with PHP and Ajax From Novice to Professional PHẦN 9

Các dữ liệu trong bảng 11-2 và 11-3, khi kết hợp, cung cấp cho một hình ảnh rất chính xác của vị trí của các đường phố và cách họ giao nhau, và không có thông tin về địa chỉ của các tòa nhà dọc theo các đường phố. Trong thực tế, một bộ kết hợp dữ liệu là những gì bạn đang có khả năng để có được từ một cơ quan điều tra dân số. | 288 CHAPTER 11 ADVANCED GEOCODING TOPICS The data in Tables 11-2 and 11-3 when combined gives a very accurate picture of the streets locations and how they intersect and yet there is no information about the addresses of the buildings along those streets. In reality a combined set of data is what you re likely to get from a census bureau. Table 11-4 gives an amalgamated view of the records from Tables 11-1 and 11-2. This is roughly the same format that the US Census Bureau provides in its TIGER Line data set which we ll introduce in the next section. Table 11-4. Road Network Chain Endpoints ID No Street Name Start Latitude Start End Longitude Latitude End Longitude Left Addr. Start Left Addr. End Right Addr. Start Right Addr. End 1000 Upper Ave 750 798 1001 Lower Ave 100 400 1002 Middle Ave 501 517 500 512 1003 West Street 1004 West Street 1005 East Street 1006 East Street You might be curious what left and right address start and end mean. Presume that you re standing on the intersection defined by a start latitude and longitude pair facing the end latitude longitude pair. From this reference point you can tell that the addresses on one side are left and the other side are right. This is how most GIS data sets pertaining to roads define left versus right. They cannot be correlated to east or west and merely reflect the order in which the points were surveyed by the municipalities. By using the start and end addresses on a street segment in conjunction with the start and end latitude and longitude you can guess the location of addresses in between. This is called interpolation and allows the providers of a data source to condense the data without a significant loss in resolution. The biggest problem arises when the size of the land divisions is