For Flask URL endpoints, GET requests are specified using the method GET. Data can be passed as an argument and accessed using request.args:

from flask import requests, jsonify
@app.route('/nba/api/v0.1/arenas', methods=['GET'])
def get_arenas():
  if 'name' in request.args:
       arenas = session.query(Arena).filter(name=request.args['name'])
  else:
       arenas = session.query(Arena).all()
  data = [{"type": "Feature",  "properties":{"name":arena.name, "id":arena.id}, 
  "geometry":{"type":"Point","coordinates":[round(arena.longitude,6), round(arena.latitude,6)]},
  } for arena in arenas]
  return jsonify({"type": "FeatureCollection","features":data})

The response data, processed into a list of Python dictionaries using a list comprehension, is added to another Python dictionary, and then converted to JSON using jsonify from Flask.