I've always wondered the same, and understood it as "owning the airspace" within the specific unit, but not having any ownership of a physical structure. No control over the maintenance of the building would be a concern -- seems very an extreme version of "neighborhood deterioration" could easily occur.

I know plenty of people in the US who own condos (usually part of a pair e.g. 1A/1B), but outside of major cities the idea of owning an "apartment" (a unit in a huge building full of hundreds of other units) is somewhat foreign. However, my relatives in eastern Europe own these types of apartments as their primary investment vehicle due to poorly performing native currency / stocks.

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via ChatGPT:

"The ownership of an apartment or condominium within a multi-unit building is indeed different from owning a single-family home. Here's how it typically works:

### Deed and Plat Map

1. *Deed*: The deed for a condominium or apartment within a high-rise will usually refer to a "unit" as defined in a "master deed" or "declaration" that has been recorded for the condominium. It will contain a description of the unit and any associated "common elements" that you may have an ownership interest in (e.g., shared hallways, gardens, and sometimes amenities like a gym or pool).

2. *Plat Map*: This would typically include a map of the entire complex, including the boundaries and location of each individual unit, along with common areas. These maps are often extremely detailed and have to be filed with a local government office.

### Ownership Structure

1. *Air Space*: In essence, you own the "air space" confined by the boundary walls of your unit, sometimes specified down to the paint on the walls. The structural elements, building exterior, and common areas are usually considered "common elements" owned collectively by all unit owners.

2. *Percentage Ownership*: Yes, you often own a percentage of the common elements, including the land upon which the building is constructed. This is sometimes proportional to the size of your unit as a percentage of the total building or complex size.

### Insurance and Liability

1. *Individual Insurance*: You would typically have a specialized form of homeowner's insurance known as an HO-6 policy that covers the internal elements of your unit (fixtures, improvements, personal property, etc.) and may provide liability coverage for incidents within your unit.

2. *Master Insurance*: The homeowners' association (HOA) will generally have a "master" insurance policy covering damage to the common elements and the overall structure. This is funded by HOA fees collected from the unit owners.

3. *Shared Risk*: The risk is essentially communal, but individual unit owners are usually responsible for the deductible on the master policy for damages originating in their units. Some complex scenarios could involve subrogation between the individual and master policies.

Understanding your specific rights and responsibilities when purchasing a unit in a multi-unit structure is crucial, and legal counsel is usually advised to navigate the complexities. Always read the declaration, by-laws, and any rules and regulations to understand your ownership fully."