The topological entropy of a continuous self-map of a compact metric space can be defined in several distinct ways; when the space is not assumed compact, these definitions can lead to distinct invariants. The original, purely topological invariant defined by Adler et. al. is infinite if the system has at least one orbit with empty limit set. The Bowen-Dinaburg formulation (based on separated sets) is equivalent to the invariant defined by Friedland (based on a compactification of the inverse limit), and dominates another invariant proposed by Bowen (maximizing dispersion rates for orbits emanating from compact subsets). Examples show that these two invariants are both heavily dependent on the uniform structure induced by the metric used to calculate them.

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