Depending on the distribution of voters for a particular party, metrics that maximize compactness can be opposed to metrics that minimize the efficiency gap. For example, in the United States, voters registered with the Democratic Party tend to be concentrated in cities, potentially resulting in a large number of "wasted" votes if compact districts are drawn around city populations. Neither of these metrics take into consideration other possible goals, such as proportional representation based on other demographic characteristics (such as race, ethnicity, gender, or income), maximizing competitiveness of elections (the greatest number of districts where party affiliation is 50/50), avoiding splits of existing government units (like cities and counties), and ensuring representation of major interest groups (like farmers or voters in a specific transportation corridor), though any of these could be incorporated into a more complicated metric.