Why does Maps load so slowly?

Location Services (including Maps and "Find My Mac") relies on a database of known Wi-Fi access points. You don't necessarily have to be connected to a wireless network, but Wi-Fi does have to be turned on and you have to be within range of one of those access points. Otherwise the machine won't be located at all, or the location will be wrong. Sometimes the location will be wrong because the database contains inaccurate data. According to reports, if you connect to a network with an iPhone, its location will be reported to Apple and added to the database after a delay. I can't confirm.

Make sure Wi-Fi is turned on. Open the Date & Time pane in System Preferences and select the Time Zone tab. If the settings are locked, click the padlock icon in the lower left corner of the window and enter your password when prompted. Then check the box marked

Set time zone automatically using current location

if it's not already checked. Within a few seconds, a red pin should drop onto the map at your location. Does that happen?