Working with vector files
Geospatial data comes in a huge variety of formats. Understanding the formats you might find in the wild, how to recognise and inspect them are key skills for geospatial analysis at the command-line. Here we'll focus on vector files.
The ~/countries directory contains 10m resolution countries data in shapefile format from Natural Earth. Shapefiles are a very common vector format for geospatial data. A shapefile is actually a .shp file and a collection of supporting files - you can see the files by running ls:
$ ls -1 countries
ne_10m_admin_0_countries.cpg
ne_10m_admin_0_countries.dbf
ne_10m_admin_0_countries.prj
ne_10m_admin_0_countries.README.html
ne_10m_admin_0_countries.shp
ne_10m_admin_0_countries.shx
ne_10m_admin_0_countries.VERSION.txt
The GDAL toolkit
The Geospatial Data Abstraction Library (GDAL/OGR) is a set of command-line utilities for working with a wide range of different raster and vector geospatial formats.
NOTE: the tools are already installed in this lesson ... but if you ever need to install them on your own machine you can use:
- OSX:
brew install gdal- Linux (Debian / Ubuntu):
sudo apt-get install gdal-bin
Getting basic information about a geospatial data file
The ogrinfo command from the GDAL toolkit allows us to find out what a geospatial vector data file contains.
NOTE: As with most UNIX commands
ogrinfohas a manpage, so you can useman ogrinfoto get detailed help at the command-line.
If we want to know what layers a file contains, we can run ogrinfo like so:
ogrinfo filepath
For example:
$ ogrinfo countries/ne_10m_admin_0_countries.shp
INFO: Open of `countries/ne_10m_admin_0_countries.shp'
using driver `ESRI Shapefile' successful.
1: ne_10m_admin_0_countries (Polygon)
ogrinfo has printed a message telling us that it successfully read the file, followed by a numbered list of layers in the file. In this case, there is only a single layer, ne_10m_admin_0_countries, which is a polygon.
You can get a full list of the formats ogrinfo can read here.