 HDC is an independent, private organization, although it works with the city government, other preservation organizations, and individual neighborhood groups.As advocate for New York's over 100 designated historic districts, HDC advises community groups about preservation issues and consults with building owners about what Landmarks Preservation Commission regulations mean.So when owners of individual landmarks or buildings in designated districts—the same regulations apply to both categories—want to make changes to their property that affect its external appearance, they must under the law apply to the LPC for approval to make those changes.