For the models, all of the field types (for example, Integer, String, and Float) are defined using SQLAlchemy ORM-column classes, except for the geometry columns, which use the GeoAlchemy2  Geometry class. The Geometry class requires a geometry type and SRID:

# Define the Arena class, which will model the Arena database table
class Arena(Base):
    __tablename__ = 'arena'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    longitude = Column(Float)
    latitude = Column(Float)
    geom = Column(Geometry(geometry_type='POINT', srid=4326))

The County class has a primary key field and a name field, as well as fields that define the many-to-one relationship with the State class. Instead of a POINT geometry type, it uses MULTIPOLYGON:

# Define the County class, which will model the County database table
class County(Base):
    __tablename__ = 'county'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    state_id = Column(Integer, ForeignKey('state.id'))
    state_ref = relationship("State",backref='county')
    geom = Column(Geometry(geometry_type='MULTIPOLYGON', srid=4326))

The District class represents US Congressional Districts. Stored with a MULTIPOLYGON geometry type and an SRID of 4326, it has a many-to-one relationship with the State class. Each district stored is linked to the state in which it resides:

# Define the District class, which will model the District database table
class District(Base):
    __tablename__ = 'district'
    id = Column(Integer, primary_key=True)
    district = Column(String)
    name = Column(String)
    state_id = Column(Integer, ForeignKey('state.id'))
    state_ref = relationship("State",backref='district')
    geom = Column(Geometry(geometry_type='MULTIPOLYGON', srid=4326))

The State class has one-to-many relationships with the County and District classes respectively, defined using the relationship function. It also has a MULTIPOLYGON geometry column with an SRID of 4326:

# Define the State class, which will model the State database table
class State(Base):
    __tablename__ = 'state'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    statefips = Column(String)
    stpostal = Column(String)
    counties = relationship('County', backref='state')
    districts = relationship('District', backref='state')
    geom = Column(Geometry(geometry_type='MULTIPOLYGON', srid=4326))

With the fields and relationships defined, the next step is to create the REST API endpoints and write the views that will query the database and return GeoJSON responses.