#### Overview of this book

QGIS is a desktop geographic information system that facilitates data viewing, editing, and analysis. Paired with the most efficient scripting language—Python, we can write effective scripts that extend the core functionality of QGIS. Based on version QGIS 2.18, this book will teach you how to write Python code that works with spatial data to automate geoprocessing tasks in QGIS. It will cover topics such as querying and editing vector data and using raster data. You will also learn to create, edit, and optimize a vector layer for faster queries, reproject a vector layer, reduce the number of vertices in a vector layer without losing critical data, and convert a raster to a vector. Following this, you will work through recipes that will help you compose static maps, create heavily customized maps, and add specialized labels and annotations. As well as this, we’ll also share a few tips and tricks based on different aspects of QGIS.

## Measuring the distance between two points

In the `QgsDistanceArea` object, PyQGIS has excellent capabilities for measuring the distance. We'll use this object for several recipes, starting with measuring the distance between two points.

If you don't already have the New York City Museums layer used in the previous recipes in this chapter, download the layer from https://github.com/GeospatialPython/Learn/raw/master/NYC_MUSEUMS_GEO.zip.

Unzip that file and place the shapefile's contents in a directory named `nyc` within your `qgis_data` directory, within your root or home directory.

### How to do it...

In the following steps, we'll extract the first and last points in the layer's point order and measure the distance between them:

1. First, import the library that contains the QGIS contents:

```        from qgis.core import QGis
```
```        lyr = QgsVectorLayer("/qgis_data/nyc/NYC_MUSEUMS_GEO.shp",
`...`