To account for core gentrification, I turned to an analysis of land values, using taxlot data to map land value per square foot. In accordance with basic urban economics theory, land values are highest in the center and descend with distance away from downtown. There are several notable localized areas of relatively high land value alongside transit corridors, including the Gateway transit center, directly to the east of I-205, where the Red, Blue, and Green MAX lines meet; and strips alongside peripheral arterials. These taxlots are, however, zoned commercially while their surrounding uses are residential, pointing to the influence of zoning on land value. These effects largely disappear when median land values are calculated for each block group in Portland; the effects of the denser, multi-directional frequent transit network, in addition to pure core proximity, appear substantially more relevant when the data is aggregated. Overall, there is a strong relationship between proximity to transit and land value at the block group level, with about 28% of the variance explained by distance from the block group center to the nearest frequent transit stop. This relationship is obviously complicated by the overlap of the two key variables in question.
The geography of land value appreciation since 1998 is quite similar to that of the 2015 value itself and is similarly correlated to transit proximity. To visualize the connection between transit and land value changes, I plotted the median land value change within a quarter mile buffer of frequent transit stops alongside all lots. The taxlots are mapped to include an equal quantity of lots within each range of values. Orange values thus represent an increase below the citywide median land value increase, while purple lots experienced above-median absolute land value appreciation. There are relatively few lots further than a quarter of a mile from frequent transit which experienced above-median appreciation during the period in question, though the decreasing impact of transit with distance from downtown is also clearly visible.