The currency heat map shows the largest rises and falls in currency pairs over the last 24 hours, identifying where trading has been most active.
You can filter the list so that it only shows the movements for a single currency such as EUR or USD. For consistency and ease of comparison, all movements will then be stated in terms of that base currency. For example, if you select USD then the list will show you the moves for USD/JPY, USD/EUR (instead of EUR/USD) so that you can more easily compare the dollar's direction against other currencies.