Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_21933 ( "Name or route" text, "type" text, "elevation groundstation" real, "elevation mountainstation" real, "slope length" real, "capacity in persons/hour" real, "construction year(s)" text )

### Question ###
Name the slope length for 1966 groundstation

### Accurate SQL ###

SELECT COUNT("slope length") FROM table_21933 WHERE "elevation groundstation" = '1966'