Navigation Stack warnings

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Hi, i am playing with the navigation stack. When i it, i am receiving some warnings.

Timed out waiting for transform from base_link to map to become available before running costmap, tf error: canTransform: target_frame map does not exist.. canTransform returned after 0.101155 timeout was 0.1.

No laser scan received (and thus no pose updates have been published) for 1515614560.495743 seconds. Verify that data is being published on the /scan topic.

What they mean? Do i have to worry about that? Also, in the second warning, i am using a fake_laser_publisher, a node from this tutorial (link).

Thanks in advance.