Note

# Introduction to GeoPandas#

This quick tutorial introduces the key concepts and basic features of GeoPandas to help you get started with your projects.

## Concepts#

GeoPandas, as the name suggests, extends the popular data science library pandas by adding support for geospatial data. If you are not familiar with `pandas`

, we recommend taking a quick look at its Getting started documentation before proceeding.

The core data structure in GeoPandas is the `geopandas.GeoDataFrame`

, a subclass of `pandas.DataFrame`

, that can store geometry columns and perform spatial operations. The `geopandas.GeoSeries`

, a subclass of `pandas.Series`

, handles the geometries. Therefore, your `GeoDataFrame`

is a combination of `pandas.Series`

, with traditional data (numerical, boolean, text etc.), and `geopandas.GeoSeries`

, with geometries (points, polygons etc.). You can have as many columns with geometries
as you wish; there’s no limit typical for desktop GIS software.

Each `GeoSeries`

can contain any geometry type (you can even mix them within a single array) and has a `GeoSeries.crs`

attribute, which stores information about the projection (CRS stands for Coordinate Reference System). Therefore, each `GeoSeries`

in a `GeoDataFrame`

can be in a different projection, allowing you to have, for example, multiple versions (different projections) of the same geometry.

Only one `GeoSeries`

in a `GeoDataFrame`

is considered the *active* geometry, which means that all geometric operations applied to a `GeoDataFrame`

operate on this *active* column.

User Guide

See more on data structures in the User Guide.

Let’s see how some of these concepts work in practice.

## Reading and writing files#

First, we need to read some data.

### Reading files#

Assuming you have a file containing both data and geometry (e.g. GeoPackage, GeoJSON, Shapefile), you can read it using `geopandas.read_file()`

, which automatically detects the filetype and creates a `GeoDataFrame`

. This tutorial uses the `"nybb"`

dataset, a map of New York boroughs, which is part of the GeoPandas installation. Therefore, we use `geopandas.datasets.get_path()`

to retrieve the path to the dataset.

```
[1]:
```

```
import geopandas
path_to_data = geopandas.datasets.get_path("nybb")
gdf = geopandas.read_file(path_to_data)
gdf
```

```
ERROR 1: PROJ: proj_create_from_database: Open of /home/docs/checkouts/readthedocs.org/user_builds/geopandas/conda/stable/share/proj failed
```

```
[1]:
```

BoroCode | BoroName | Shape_Leng | Shape_Area | geometry | |
---|---|---|---|---|---|

0 | 5 | Staten Island | 330470.010332 | 1.623820e+09 | MULTIPOLYGON (((970217.022 145643.332, 970227.... |

1 | 4 | Queens | 896344.047763 | 3.045213e+09 | MULTIPOLYGON (((1029606.077 156073.814, 102957... |

2 | 3 | Brooklyn | 741080.523166 | 1.937479e+09 | MULTIPOLYGON (((1021176.479 151374.797, 102100... |

3 | 1 | Manhattan | 359299.096471 | 6.364715e+08 | MULTIPOLYGON (((981219.056 188655.316, 980940.... |

4 | 2 | Bronx | 464392.991824 | 1.186925e+09 | MULTIPOLYGON (((1012821.806 229228.265, 101278... |

### Writing files#

To write a `GeoDataFrame`

back to file use `GeoDataFrame.to_file()`

. The default file format is Shapefile, but you can specify your own with the `driver`

keyword.

```
[2]:
```

```
gdf.to_file("my_file.geojson", driver="GeoJSON")
```

User Guide

See more on reading and writing data in the User Guide.

## Simple accessors and methods#

Now we have our `GeoDataFrame`

and can start working with its geometry.

Since there was only one geometry column in the New York Boroughs dataset, this column automatically becomes the *active* geometry and spatial methods used on the `GeoDataFrame`

will be applied to the `"geometry"`

column.

### Measuring area#

To measure the area of each polygon (or MultiPolygon in this specific case), access the `GeoDataFrame.area`

attribute, which returns a `pandas.Series`

. Note that `GeoDataFrame.area`

is just `GeoSeries.area`

applied to the *active* geometry column.

But first, to make the results easier to read, set the names of the boroughs as the index:

```
[3]:
```

```
gdf = gdf.set_index("BoroName")
```

```
[4]:
```

```
gdf["area"] = gdf.area
gdf["area"]
```

```
[4]:
```

```
BoroName
Staten Island 1.623822e+09
Queens 3.045214e+09
Brooklyn 1.937478e+09
Manhattan 6.364712e+08
Bronx 1.186926e+09
Name: area, dtype: float64
```

### Getting polygon boundary and centroid#

To get the boundary of each polygon (LineString), access the `GeoDataFrame.boundary`

:

```
[5]:
```

```
gdf['boundary'] = gdf.boundary
gdf['boundary']
```

```
[5]:
```

```
BoroName
Staten Island MULTILINESTRING ((970217.022 145643.332, 97022...
Queens MULTILINESTRING ((1029606.077 156073.814, 1029...
Brooklyn MULTILINESTRING ((1021176.479 151374.797, 1021...
Manhattan MULTILINESTRING ((981219.056 188655.316, 98094...
Bronx MULTILINESTRING ((1012821.806 229228.265, 1012...
Name: boundary, dtype: geometry
```

Since we have saved boundary as a new column, we now have two geometry columns in the same `GeoDataFrame`

.

We can also create new geometries, which could be, for example, a buffered version of the original one (i.e., `GeoDataFrame.buffer(10)`

) or its centroid:

```
[6]:
```

```
gdf['centroid'] = gdf.centroid
gdf['centroid']
```

```
[6]:
```

```
BoroName
Staten Island POINT (941639.450 150931.991)
Queens POINT (1034578.078 197116.604)
Brooklyn POINT (998769.115 174169.761)
Manhattan POINT (993336.965 222451.437)
Bronx POINT (1021174.790 249937.980)
Name: centroid, dtype: geometry
```

### Measuring distance#

We can also measure how far each centroid is from the first centroid location.

```
[7]:
```

```
first_point = gdf['centroid'].iloc[0]
gdf['distance'] = gdf['centroid'].distance(first_point)
gdf['distance']
```

```
[7]:
```

```
BoroName
Staten Island 0.000000
Queens 103781.535276
Brooklyn 61674.893421
Manhattan 88247.742789
Bronx 126996.283623
Name: distance, dtype: float64
```

Note that `geopandas.GeoDataFrame`

is a subclass of `pandas.DataFrame`

, so we have all the pandas functionality available to use on the geospatial dataset — we can even perform data manipulations with the attributes and geometry information together.

For example, to calculate the average of the distances measured above, access the ‘distance’ column and call the mean() method on it:

```
[8]:
```

```
gdf['distance'].mean()
```

```
[8]:
```

```
76140.09102166798
```

## Making maps#

GeoPandas can also plot maps, so we can check how the geometries appear in space. To plot the active geometry, call `GeoDataFrame.plot()`

. To color code by another column, pass in that column as the first argument. In the example below, we plot the active geometry column and color code by the `"area"`

column. We also want to show a legend (`legend=True`

).

```
[9]:
```

```
gdf.plot("area", legend=True)
```

```
[9]:
```

```
<AxesSubplot: >
```

You can also explore your data interactively using `GeoDataFrame.explore()`

, which behaves in the same way `plot()`

does but returns an interactive map instead.

```
[10]:
```

```
gdf.explore("area", legend=False)
```

```
[10]:
```