Good Grief, I agree that development is not bad for a neighborhood. Gentrification(), however, involves displacement of the new residents of the neighborhood.

This is my understanding of what happens when a neighborhood gets hip and very expensive condo's or other housing starts getting built.

The City Assessor evaluates properties every three years (I think), and assigns a property value to the property based on approximate value of the building, housing supply and demand, location, structure, the age of the building etc.

I think that when a neighborhood becomes desirable

(for example: because of factors such as desirable architecture, proximity to cultural attractions such as theaters, or a nearby booming restaurant strip. These factors are probably combined with other factors such as the migration patterns of suburban baby boomers children, people from the middle or upper class moving from one part of the city to another, or empty nester suburbanites moving out of high matainence suburban homes whose size they no longer can justify)

it starts getting eyed by developers. Someone takes a chance and builds an expensive condo. Other developers follow their lead. The presence of nearby condominium developments drive up the property value of the surrounding homes. A rising property value is directly correlated to higher property taxes. Renters of housing units in the area have their rents raised by landlords who need or want to pass off the burden of the higher taxes. Some landlords may also decide to take their building "condo," and residents who cannot afford to purchase condominium units must move out of the building after a period of time. Eventually rent and property taxes in the area gets so high in a neighborhood that the original residents must move out as new wealthier residents move in, or families and individuals must pay well over their means for housing.

Development could be a positive thing in a neighborhood if steps are taken to ensure that it does not spawn a wave of gentrification, like creating a permanent stock of affordable housing to ensure that the original residents are not displaced and creating a planned development process that all resident of the neighborhood are a part of.

I guess, "Develop, Not Displace!" could be a good slogan for that mess of writing up there. I hope that helps, and if I am completely wrong someone let me know.