Shapefiles

This page provides an in-depth guide to using shapefiles in PoliSciPy to create election maps. You’ll learn what shapefiles are, how to load them, and how to integrate them with election data for visualization.

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Working with Shapefiles in PoliSciPy

Shapefiles are the foundation of electoral college map visualizations in PoliSciPy. They contain the geographic and boundary information necessary to render the polygons representing states, territories, and other regions of the map. This section explains the structure of shapefiles, how to load and process them, and how to integrate election data for subsequent visualization. First it might be helpful to understand:

What is a Shapefile?

A shapefile is a widely used geospatial vector data format for geographic information system (GIS) software. It represents geographic features (e.g., states, counties) and their attributes. A shapefile typically consists of several files with the same name but different extensions, including:

• .shp: Contains geometry data (shapes of features).

• .shx: An index file to improve access to geometry data.

• .dbf: A database file storing attribute data for each feature (e.g., state names, FIPS codes).

Note on Shapefiles:

PoliSciPy uses modified shapefiles originally provided by the United States Census Bureau through the TIGER/Line dataset. For more information about the original shapefiles and how to access them, please visit the citation page.

Inspecting the Shapefile

You can inspect the shapefile once you’ve loaded it using the load_shapefile() method. If you type the following:

gdf = load_shapefile()
gdf.head(2)

You can then inspect the shapefile shown below. A full list of all of the columns included in the shapefile is shown below.

STATEFP	NAME	STUSPS	elec_votes_2024	defectors	defector_party	centroid_x	centroid_y	geometry
28	Mississippi	MS	6	0	None	-89.6652	32.7509	MULTIPOLYGON
37	North Carolina	NC	16	0	None	-79.3724	35.5415	MULTIPOLYGON

Understanding the Shapefile’s Columns

For more information on the columns in the shapefile and their meanings, you can inspect the shapefile’s schema. Each row in the shapefile represents a U.S. state or territory and includes the following columns:

Column	Type	Description
STATEFP	str:2	The two-digit FIPS code assigned to the state.
STATENS	str:8	A unique identifier for the state in the GNIS database.
AFFGEOID	str:11	An 11-character unique geographic identifier.
GEOID	str:2	The numeric FIPS code (same as STATEFP). See: What are GEOIDs?
STUSPS	str:2	The two-letter postal abbreviation for the state (e.g., CA, TX).
NAME	str:100	The full state name (e.g., “California”).
LSAD	str:2	Legal/statistical area description (usually empty or generic for states).
ALAND	int:14	Land area of the state in square meters.
AWATER	int:14	Water area of the state in square meters.
centroid_x	float:19.11	Longitude coordinate of the state’s centroid.
centroid_y	float:19.11	Latitude coordinate of the state’s centroid.
elec_votes	int:5	The number of electoral votes assigned to the state.
geometry	Polygon	The geographic shape of the state as a polygon.

This table serves as a reference for understanding the attributes in the shapefile and how they can be used when merging data or visualizing maps.

Next Step: Merging Election Data with the Shapefile

Next, we’ll explore how to merge additional election data with the shapefile for visualization. Head over to the next section on Merging Data to learn more about integrating datasets for analysis and creating visualizations.