Filtering

Filtering and Urban Social Geography

Filtering as a process of urban social geographic change is commonly associated with the Chicago School of urban studies, particularly Ernest Burgess's 1925 model of urban concentric zones, and even more so with Homer Hoyt's 1939 model of sectoral land use patterns, though observations of the phenomenon predate these models. Urban growth takes place largely in the periphery, where the well-off move to new housing, leaving vacancies that become housing opportunities for households lower down the escalator. These models highlight a spatial dimension of filtering as an outward movement of households generated by new construction, as vacancies move in the opposite direction, ending in low-status neighborhoods in the inner city. The Chicago School, employing concepts of invasion and succession borrowed from ecology, emphasized the push factor of immigrants to the city center creating outward ripples in the urban social geographic fabric. Hoyt instead emphasized market mechanisms, the generative force of upper-echelon demand for new modern dwellings in the periphery, and the opportunities this demand spawned through chains of moves.

Filtering and Gentrification

Filtering is the opposite of gentrification, both at the microlevel of individual moves and at the scale of neighborhoods, both as a pattern of residential mobility and in terms of investment contra disinvestment in buildings. As a particular event, filtering can be said to take place when the household that moves into a dwelling is of lower socioeconomic status than the household that moves out, while gentrification takes place when the household that moves into a vacancy is of higher socioeconomic status than the household that vacates the dwelling. Though individual changes in occupancy—housing turnover—can be classified as filtering or gentrification, understandings and explanations of these processes of urban change extend beyond the particular, to social structures and mechanisms underlying neighborhood change, housing market dynamics, housing policies, urban politics, and the political economy of space.

Filtering as neighborhood change is characterized by a downward shift in the socioeconomic status of residents through in- and out-migration and by downward movement in relative property values, commonly associated with redlining (designation of the area by financial institutions as ineligible for loans) and disinvestment (e.g., minimal or no maintenance and repair). Gentrification on the other hand is characterized by an upward shift in the socioeconomic status of residents and reinvestment in buildings.

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