For MyISAM and (as of MySQL 5.7.5) InnoDB tables, MySQL can create
spatial indexes using syntax similar to that for creating regular
indexes, but using the SPATIAL keyword. Columns in spatial indexes must
be declared NOT NULL. The following examples demonstrate how to create
spatial indexes:

o With CREATE TABLE:

CREATE TABLE geom (g GEOMETRY NOT NULL, SPATIAL INDEX(g)) ENGINE=MyISAM;

o With ALTER TABLE:

ALTER TABLE geom ADD SPATIAL INDEX(g);

o With CREATE INDEX:

CREATE SPATIAL INDEX sp_index ON geom (g);

SPATIAL INDEX creates an R-tree index. For storage engines that support
nonspatial indexing of spatial columns, the engine creates a B-tree
index. A B-tree index on spatial values is useful for exact-value
lookups, but not for range scans.

For more information on indexing spatial columns, see [HELP CREATE
INDEX].

To drop spatial indexes, use ALTER TABLE or DROP INDEX:

o With ALTER TABLE:

ALTER TABLE geom DROP INDEX g;

o With DROP INDEX:

DROP INDEX sp_index ON geom;

Example: Suppose that a table geom contains more than 32,000
geometries, which are stored in the column g of type GEOMETRY. The
table also has an AUTO_INCREMENT column fid for storing object ID
values.

URL: http://dev.mysql.com/doc/refman/5.7/en/creating-spatial-indexes.html

