You are given the following sketch of a surface weather map. The thick, dark line represents a front that separates contrasting air masses (cold to the north and warm to the south). The observed, low-level winds are indicated on the cold and warm sides of the front. You would categorize the boundary between air masses as a front.

front air masses

Explanation: The masses have fairly uniform temperature and moisture content in horizontal direction but its not uniform in vertical.

They are usually characterized by their temperature and humidity properties.

The properties in which air masses are usually determined by the the underlying surface properties where they come from. And immediately formed, air masses migrate within the general circulation. Also Upon movement, air masses displace residual air over locations thus changing temperature and humidity characteristics. Moreover it Contain uniform temperature and humidity characteristics.

Warm Front

Explanation:

Warm front- a front in which warm air replaces cooler air at the surface and some of the characteristics of warm fronts include the slope of a typical warm front is 1:200 (more gentle than cold fronts) and Warm fronts tend to move slowly.