system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did the US choose Hiroshima and Nagasaki to be bombed rather than Tokyo or some other major city?
gpt
The work on the actual selection of targets for the atomic bomb was begun in the spring of 1945. This was done in close cooperation with the Commanding General, Army Air Forces, and his Headquarters. A number of experts in various fields assisted in the study. These included mathematicians, theoretical physicists, experts on the blast effects of bombs, weather consultants, and various other specialists. Some of the important considerations were:

The range of the aircraft which would carry the bomb.

The desirability of visual bombing in order to insure the most effective use of the bomb.

Probable weather conditions in the target areas.

Importance of having one primary and two secondary targets for each mission, so that if weather conditions prohibited bombing the target there would be at least two alternates.

Selection of targets to produce the greatest military effect on the Japanese people and thereby most effectively shorten the war.

The morale effect upon the enemy.

These led in turn to the following:

Since the atomic bomb was expected to produce its greatest amount of damage by primary blast effect, and next greatest by fires, the targets should contain a large percentage of closely-built frame buildings and other construction that would be most susceptible to damage by blast and fire.
The maximum blast effect of the bomb was calculated to extend over an area of approximately 1 mile in radius; therefore the selected targets should contain a densely built-up area of at least this size.
The selected targets should have a high military strategic value.
The first target should be relatively untouched by previous bombing, in order that the effect of a single atomic bomb could be determined.



The U.S. decided to drop the bombs onto military industrial targets and centers that had significant military utility such as ports and airfields. Nagasaki was actually a secondary target, being a major port. Inclement weather kept the Bockscar from dropping the second atomic bomb on Kokura.
Hiroshima, the first city, was "an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focussing[sic] effect which would considerably increase the blast damage. 

---  Reasons for NOT nuking Tokyo ----

The weather records showed that for five years there had never been two successive good visual bombing days over Tokyo, indicating what might be expected over other targets in the home islands. The worst month of the year for visual bombing was believed to be June, after which the weather should improve slightly during July and August and then become worse again during September. Since good bombing conditions would occur rarely, the most intense plans and preparations were necessary in order to secure accurate weather forecasts and to arrange for full utilization of whatever good weather might occur. It was also very desirable to start the raids before September.
The U.S. likely did not target Tokyo for the atomic bomb strikes as it was the seat of the Emperor and the location of much of the high ranking military officers. These are precisely the people you do not want to kill if you want to negotiate a surrender, as they are the people you would be negotiating with.