Improved resolution in this context means more detail in an image or map or graphical representation. In this case the third-generation "HapMap" is more detailed than previous first and second generation maps of human genetic variation.
Consider (7) and (12) below.
Quote:
resolution
1.
a formal expression of opinion or intention made, usually after voting, by a formal organization, a legislature, a club, or other group.Compare concurrent resolution, joint resolution.
2.
a resolve or determination: to make a firm resolution to do something.
3.
the act of resolving or determining upon an action or course of action, method, procedure, etc.
4.
the mental state or quality of being resolved or resolute; firmness of purpose.
5.
the act or process of resolving or separating into constituent or elementary parts.
6.
the resulting state.
7.
Optics. the act, process, or capability of distinguishing between two separate but adjacent objects or sources of light or between two nearly equal wavelengths.Compare resolving power.
8.
a solution, accommodation, or settling of a problem, controversy, etc.
9.
Music.
a.
the progression of a voice part or of the harmony as a whole from a dissonance to a consonance.
b.
the tone or chord to which a dissonance is resolved.
10.
reduction to a simpler form; conversion.
11.
Medicine/Medical. the reduction or disappearance of a swelling or inflammation without suppuration.
12.
the degree of sharpness of a computer-generated image as measured by the number of dots per linear inch in a hard-copy printout or the number of pixels across and down on a display screen.
http://dictionary.reference.com/browse/resolution