Читать книгу The GIS 20 - Gina Clemmer - Страница 8

Shapefiles are the maps behind the maps. You need them, and you need to know a few things about them. You need to know how fresh the shapefile is (is it from 2016 or 1972?), how much it costs to get your hands on it (free or $2,000? Makes a difference), and how accurate it is (drawn by fifth-graders or NASA?). The US Census Bureau is an outstanding resource for shapefiles. It updates them every year, they cost zero dollars, and they are pretty accurate.

The US Census Bureau is the national custodian of geographic definitions of US borders. It is the agency in charge of keeping the official latitude-longitude boundaries of all states and the US as a whole.

In the following chapters, and in life in general, you will need shapefiles to create maps. Two useful shapefiles are counties and cities. You can download these two now. But first, you will need a place to save your files.