Google appears to think of ranking in terms of zones, where the first zone features the best possible mix of proximity, relevance, and prominence, and the second zone begins to sacrifice either proximity, or relevance, or both, but is less likely to sacrifice prominence. In more human terms, this means that Google wants to show us the best options for a query, and when it runs of inventory, it brings in results that are farther away or that might offer a reasonable alternative.
Ranking Correlations with Other Reputation and Search Metrics Are Not Linear
Google appears to think of ranking in terms of zones, where the first zone features the best possible mix of proximity, relevance, and prominence, and the second zone begins to sacrifice either proximity, or relevance, or both, but is less likely to sacrifice prominence. In more human terms, this means that Google wants to show us the best options for a query, and when it runs of inventory, it brings in results that are farther away or that might offer a reasonable alternative.