 geo_point field does not support GeoJson which can be a PITA if your data is in such a format. Indexing it as a geo_shape is an option but very wasteful.
server/src/test/java/org/elasticsearch/index/search/geo/GeoUtilsTests.java
private static final char[] BASE_32 = {
        '0',
        '1',
        '2',
        '3',
        '4',
        '5',
        '6',
        '7',
        '8',
        '9',
        'b',
        'c',
        'd',
        'e',
        'f',
        'g',
        'h',
        'j',
        'k',
        'm',
        'n',
        'p',
        'q',
        'r',
        's',