Since there are many Guatemala departments (similar to states or provinces), in the interest of helping the pages load faster, this section is divided into three pages. Here's a list of all the departments so you can simply click on the name of the department to be taken to a specific department review, or click on the department on the map - the numbers correspond to the names on the numbered list. The first column goes to the first page, the second column stays on this page, and the third, to the third.
Note: This review is about the Department of Guatemala, not Guatemala City, which will be covered separately.
As can be expected with the department that includes Guatemala City, Google Maps does a decent job covering the major roads of the department of Guatemala. The major highways that run through it are CA-9, CA-1, Hwy 5, as well as major offshoots of these. Hwy 5 seems to disappear for a bit between San Juan Sacatepéquez and Chajmaic, though it's definitely a road that's in service. CA-1 and CA-9 to the west and southwest of the capital, respectively, are both adequately marked, as well as CA-1 coming south out of the capital that joins with CA-9 east of Amatitlán and heads to El Salvador. Hwy 18 to the east of the capital heading into the department of Jalapa is also clearly marked (though quite curvy!) CA-9 heading northeast toward Honduras is also good. In all, this is one of the more useful departmental maps on Google Maps, though some of the smaller roads are harder to find. This map can definitely be used to plan a route, even within the capital, and is accurate in its own way, with a bit of creative interpretation.
Major Cities: Guatemala City, Villanueva, Mixco, San Pedro Sacatepéquez, San Juan Sacatepéque, San Raimundo
The Department of Huehuetenango is a section of the country that doesn't get a whole lot of attention, and this goes for Google Maps, as well. On a recent driving expedition to Huehuetenango from the capital, I checked out the map on Google, and found it to be almost useless for anything beyond actually getting to the town of Huehuetenango. CA-1 is marked going to the border, and smaller roads go north from Huehuetenango (Hwy 9N). However, next to no attention is given to areas between the two highways, even to such tourist destinations such as Todos Santos. This map won't help you out in Huehuetenango.
Major cities: Huehuetenango, Todos Santos Cuchumatán, Jacaltenango
Google Maps does a good job on the Department of Izabal, mainly because this department does not have many roads to start with, as it has quite a bit of water. The major roads (Hwy 5 and CA-9) are marked. Livingston could be given more prominence, as it is a common destination that is generally reached by water from Puerto Barrios (Google Maps shows small roads going that direction, but I've never tried them out), but instead you have to zoom in quite a bit to see it.
Major Cities: Puerto Barrios, Livingston, Rio Dulce
The Google Map of the Department of Jalapa is quite good, showing more secondary roads that even a couple of in-depth paper maps I have. Hwy 18 (east/west) and Hwy 19 (north/south) are clearly and accurately marked. Though the secondary roads on Google maps are not numbered, they are quite extensive and useful.
The Department of Jutiapa, bordering El Salvador, is represented fairly well on Google Maps, but there are some discrepancies in highway names that are important to be aware of. I cannot find any other verification that Hwy 2, which appears along CA-1, is called that in reality. Also, Hwy 22, breaking off of CA-1/Hwy 2, is better known as CA-8, which continues to El Salvador, running parallel to CA-1 to the north and CA-2 to the south. The rest of the map seems to be ok, with the Google Maps standard lack of numbering secondary roads.
The Google Maps rendition of the Department of Quetzaltenango is pretty good. I'm not sure if Google takes into account tourism when updating its maps, but it seems to me that the touristy places in Guatemala have more detail. Hopefully the rest gets updated sooner rather than later. As it is, the major roads are nicely labeled on Google Maps and the secondary roads are present, if not labeled (though some are). This map will be useful for you.
As with some of the other coastal departments, the department of Retalhuleu is heavy on water and light on roads, so Google Maps does ok on this one. The major cities and roads are labeled, with a slight discrepancy: Google Maps has Hwy 11 changing to 9S when it crosses CA-1 heading north. In reality, it's 9S all the way to the coast.
The department of Sacatepéquez, with its funny-sounding name (not be confused with Suchitepéquez), is a department that I would daresay most extranjeros become at least somewhat familiar with during their stay in Guatemala. As with other touristy departments, Google Maps has done a okay job on its map for Sacatepéquez. CA-1 coming out of the capital to San Lucas crosses Hwy 10 going south - you can't miss the big "Antigua Guatemala" signs. Nice roads around here. Though this map will get you to key cities in Sacatepéquez, I wouldn't trust it to get you around any specific cities. As you can see when you zoom in, there is next to no detail for cities. Can't have everything, eh?
Major cities: San Lucas, Antigua, Jocotenango, Ciudad Vieja, Sumpango