Format: 

Lastname, Firstname, cartographer. Title of Map. Publisher, Day Month, Year. Map. Database Name or Title of Non-Publisher Website, DOI or URL. Accessed Day Month Year.

Lastname, Firstname, cartographer. Title of Map. Publisher, Day Month, Year. Map. Database Name or Title of Non-Publisher Website, DOI or URL (when accessed from the publisher's website). Accessed Day Month Year. Map.

Lastname, Firstname, cartographer. Title of Map. Publisher, Day Month, Year. Map.

Examples: 

Poverty Rate by Census Tract: Hurricane Katrina Disaster Areas Louisiana, Mississippi, and Alabama Region. Sept. 2005. United States Census Bureau, www2.census.gov/geo/maps/special/HurKat_Orig/Katrina_Poverty_Rate.pdf. Accessed 28 July 2015. Map.

In-text: (Poverty Rate)

Rochester, NY. Google Maps, goo.gl/maps/hQNyouiux6A2. Accessed 29 July 2015. Map.

In-text: (Rochester, NY)

Notes: 

Maps should be treated as standalone entities, similar to a book. You may choose to provide a descriptive label (e.g. cartographer) for the author when appropriate (MLA 23-24). For electronic sources, if the publisher for the map is already sufficiently represented by the title of the website, you can omit the publisher (see second example) (MLA 42). It is recommended that you include an access date, particularly for maps that are dynamic and may change (e.g. Google Maps) (MLA 53). You may also choose to include Map at the end of your reference to specify the type of source you are citing as it may not be apparent from the rest of the citation alone (MLA 52).

Source:

This source type is not covered by the MLA Handbook (8th ed.)