In a map campiagn there is a map(usually a city) that is divied into sectors. At the beggining of the game you and you opponent(s) get a certain amount of coloured pins that you can place in any sectors you want(one pin for each sector). Then as the campaign starts you and your opponents will place more pins down onto the map as you gain territory BUT if you and your opponent place a pin in the same sector then you battle over it. This battle can include cleanse missions, night fight, whatever basically. Whoever wins the battle gets to place their pin in the sector. Also, the campaign organiser will usually make special rules for certain sectors for example the city square may have a statue that ups initiative and whoever controls the city square gets 1+ initiative as long as he controls it.