What's the difference between "am Zentrum" and "im Zentrum"

Question

Can you tell me the difference between these sentences, especially the prepositions:

1. Ich arbeite als Arzt am Zentrum der Uni.
2. Ich arbeite als Arzt im Zentrum der Uni.

And these two sentences:

1. Ich arbeite in der privaten Klinik
2. Ich arbeite an der privaten Klinik.

Answer 1

In these examples, "in" ("in der", "im" [= "in dem"]) indicates primarily the location where somebody works, whereas "an" ("an der", "am" [= "an dem"]) indicates primarily the organization or the employer. Since a hospital or a university is both an employer and a location, both prepositions can be used.

Note that the use of "an" with schools, universities, or hospitals could be considered as an exception. For most employers, one uses "bei", rather than "an" ("Ich arbeite bei Siemens / beim Finanzamt / bei der Sparkasse").