The Seoul Metropolitan government defines the hanok protection areas of Bukchon as follows (this information comes from the page 106 of Bukchon Preservation plan published in December 2001 click to see the original text in Korean: HTML or PDF)

An area containing more than 20 hanoks is a protection area.  There are two categories of protection areas: ordinary protection areas and special protection areas.

Qualification as a special protection area is determined by the quality of the hanoks, the purpose (zoning) of the hanok, the registration of the hanok, whether the hanok is owned by the Seoul Metropolitan Government, whether the hanok is owned by a civilian organization, etc. 

A special protection area has more than 50 hanoks, more than 50% are residential hanoks, less than 25% are hanoks in poor condition, and the average size of a hanok must be more than 177 square meters.  This area should receive special protection.

An ordinary protection area has more than 20 hanoks, and the average size must be 115 square meters. 

There are 3 special protection areas in Bukchon, whose total area is 54,000 square meters. 

There are 7 ordinary protection areas in Bukchon, with a total area of 61,000 square meters.

Hanok Special Protection Area (한옥특별관리구역)

The three special protection areas are Kahoi Dong 31 (S1), Kahoi Dong 11 (S2), and Kay Dong Inchon Memorial Area (S3).

In 2001, the percentage of hanoks (authentic hanoks and nearly authentic hanoks) in each special protection area is 95% in S1, 73% in S2, and 69% in S3. 42% of the hanoks in S1 were in very good condition, 41% were in average condition, and 17% were in poor but livable condition. 

Also in S2, 24% of the hanoks were in very good condition, 52% were in average condition, 22% were in poor but livable condition, and there were fewer hanoks in good condition than in S1. 

In S3, 33% of the hanoks were in very good condition, 41% were in average condition, and 26% were in poor but livable condition, also in 2001.