Anonymous
Estimating the market size should be akin to a back-of-the-envelope type of calculation. Since there's already data from the United States available, you could calculate the proportion of active users for urban, rural and suburban areas. In other words, you segment the country into those 3 areas, and calculate the average proportion of the population that uses DoorDash. Now, the rest of the problem is solved by getting demographic data for each of these segments in the U.K. and multiplying by expected proportions, then summing the products. Besides U.S. data, you may want to look at another Anglo country, like Canada or Australia to come up with a few estimates (if the data is available). For these estimates based on Canada, Australia and the U.S., you could simply take the median of each estimate to arrive at your final number.
