Normally, to see what another race has built on the tiles of one of their planets, you need a 'High' espionage level with the race in question.

However, with the spy system, you can totally bypass that requirement. To do it, make sure you have at least one spy available for deployment, click on the deploy spy button, and click on the planet you want to look at. You don't even have to actually deploy that spy. With this method, the player can look at the improvements built on any foreign planet they've discovered.

Unless something is changed, there's currently no point in requiring the high espionage level to look at a foreign planet's development.