Estimation of urban population by means of satellite images.

Refer to the Geographical Analysis (Jan. 2007) study that demonstrated the use of satellite image maps for estimating urban population, presented in Exercise 12.18

(p. 698). A first-order model for census block population density (y) was fit as a function of the proportion of a block with low-density residential areas 1x12 and the proportion of a block with high-density residential areas 1x22. Now consider a complete second-order model for y.

a. Write the equation of the model.

b. Identify the terms in the model that allow for curvilinear relationships.