If other factors such as vehicles, factories, and population were ignored, the area that would be the warmest on a typical summer day would be the area with the lowest surface albedo, as it would absorb more sunlight and convert it to heat.
Surface albedo is a measure of how much solar radiation is reflected by a surface. Surfaces with high albedo, such as snow and ice, reflect more solar radiation and absorb less heat, while surfaces with low albedo, such as asphalt and dark soil, absorb more solar radiation and convert it to heat.
Therefore, on a typical summer day, the area with the lowest surface albedo, such as an urban area with many dark surfaces like asphalt and buildings, would be the warmest. Conversely, areas with high surface albedo, such as snow-covered mountains or white sandy beaches, would be relatively cooler.