I know what you’re thinking – “Summer is coming up – shorts are what you wear in summer!” Stay with me for a minute. One of the principles of one bag travel is to have clothing that can be worn under multiple conditions. Each piece has to work for its space in the carry on bag. Do shorts really do that? Men can get more than one use out of shorts by wearing them as swim trunks. Shorts are dual use for them. But women? Not so much. On top of that, many cultures consider shorts as beach wear. You can’t wear them anywhere else. Fortunately, there are a lot of cute alternatives to shorts.
Capri Pants – Capri pants are nice because they are considered equal to pants in many cultures. They can be dressed up with a nice top and shoes for dinner. They can be dressed down with a T-shirt and casual shoes for outdoors activities. Surprisingly, they are almost as cool as shorts. The air can still move around your feet. Stay away from heavy cotton – it is oppressive in summer humidity.
Skirts – Many women hate skirts and I’m not sure why. They give you a certain level of respectability. This is not a bad thing when dealing with shop keepers and hotel desk clerks! Like capri pants, they can be dressed up or down. In a really hot climate they allow the cool breezes to swirl through your legs. I think this makes them cooler than shorts. One of the key issues with skirts is finding the correct cut and hem line so that they flatter your figure. Skirts that fall at or below the knee are a better fit culturally. I like to bring reversible skirts so I get more fashion choices. Several are made out of georgette, so they are especially cool. Georgette also washes and dries quickly, making it great for travel.
Skorts – I really like skorts – as long as they have the right cut. Knee length skorts can have the same level of dressiness as a skirt. They can be dressed up or down. One of my favorite skorts is the “Whatever” skort from Athleta. It is made from a rugged wicking material that can handle a hike in the jungle. It will wash and dry quickly. It comes in petite, regular, and tall sizes. Just about perfect. Athleta has stopped making these shorts but there are usually several on sale on E-bay.
Update on July 2, 2015 – Added note that Athleta Whatever skorts are still available on E-bay.
Lady Light Travel 
“Many women hate skirts and I’m not sure why” – I can answer you in all honesty: I hate the feeling of my skin touching another part of my skin. So wearing a skirt (or a dress for that matter) is unbearable (or I have to seat with my legs spread wide so that they never touch each other). I also dislike skirts because they restrict the possibility of what you can do without being considered weird and unfit for social life: sometimes while travelling you have to climb up (’cause someone locked the entry and forgot the key to the gate or the other way is prohibitively longer) and doing it while showing the whole world your underwear is considered inappropriate (I don’t care but I know others will do and I don’t want to offend them).
I normally delete anonymous posts from randomized ip addresses but I do believe your comment merits a reply.
Skirts and dresses were the only garments allowed for girls at my school. I can assure you that I climbed trees, fences, and monkey bars without exposing body parts. A looser knee length skirt usually provides enough coverage for this activity unless it is quite windy. Even then, there are other solutions to the coverage/skin problem. You could wear a pair of loose bike shorts under your skirt instead of a slip. Many skorts incorporate this same idea. You could also wear a split-skirt slip or a skimmie under your skirt. Both the bike shorts and split slip protect the skirt from sweat, allowing it to stay clean longer.
If you really don’t want to offend people then stay away from shorts. They just aren’t appropriate in many countries. Most of the locals won’t tell you that they are offended but they will withdraw. This makes it difficult to connect with others and forge relationships.
Similar to the other poster, I also see a role for shorts in my onebag packing list. I LOVE your 3-tier packing formula by the way, and have adapted it for my own use. I add shorts to the second “temperature” tier of my list; I see shorts and a tank top as the warm-weather counterpart to a thermal top and leggings in cold weather. I make the shorts multi-use by using them to exercise, hike, lounge, or sleep in. To your point, I’d be unlikely to wear them in the city.