Residential only–or not?

In the early days of Metro Manila, certain areas/streets were initially considered for residential use only. You'll see this in the annotation in the title.

For example, titles of properties in certain areas in Mandaluyong would have an annotation restricting all developments to be mainly for residential purposes only (e.g., no commercial).

Then, one day, one entrepreneurial owner converts his house into a store. Then someone puts up a car wash. Then someone puts up a restaurant.

Over time, these areas have become bustling streets filled with commercial establishments. Examples are Examiner St. in Quezon City, Aguirre St. in Paranaque, and West Capitol Drive in Pasig. Up to now, you'll still see some old houses on these streets.

So, how do you know if you could create a commercial structure on these streets? Do you assume you could create a commercial structure since others have done it? Will the annotation on the title cause problems later on if you do?

The answer to these questions is the city's zoning ordinance.

The city's zoning ordinance (ZO) is the classification determined by the local government. The ZO will determine what an owner could use the property for and what type. For example, it could be R-1, R-2, or C-1, C-2. The letter pertains to the class (i.e., residential, commercial, industrial), and the number refers to the kind of structure that could be built (2-story house vs. 4 stories).

If a zoning ordinance says commercial structures may be built, it supersedes the annotation on the title–provided the ordinance was set on a later date.

You can get the zoning ordinance from the City Assessor's office.

Thanks to @bucketlease for clarifying this.