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 stays on this page, the second column takes you to the second page, and the third, to the third.
When you look at the Alta Verapaz Google Map, the department boundaries are clearly marked and major highways are listed, but only a few cities show. As you zoom in, more towns show up, but very few extra roads show. In fact, most of the roads that show up are very close to the main highway and are not numbered. This is a mostly rural area with the main attraction being Cobán. Still, the fact that certain important cities aren't visible, such as Fray Bartolomé de las Casas, where there's a regional airport, is disappointing.
Major Cities: Cobán, San Pedro Carchá, Fray Bartolomé de las Casas
Baja Verapaz is a smaller department, and the main highways (5 and 17) are clear enough, and department boundaries are easy to find. Though the smaller roads are not numbered, you can see them (don't confuse them with waterways!) enough to tentatively plan your driving route. Salamá, the main city in this department, has decent street map detail.
The department of Chimaltenango, luckily for the Google Maps viewer, sits between the capital and a gringo hangout, Lake Atitlán, and also has heavy traffic to the border with Mexico and the Highlands. All this makes for lots of roads, and of these, the majors ones are listed (Hwy 1 towards Panajachel and CA-1, the Panamerican Highway). Zooming in further, there are lots of other roads, and a couple are even labeled. Overall, this Google Maps is pretty useful for this department, as long as you aren't getting too far off the beaten path.
Major Cities: Chimaltenango, San Martín Jilotepeque
The department of Chiquimula, which borders both Honduras and El Salvador, is labeled pretty well, with all major roads being numbered and the smaller roads being adequately represented, though not numbered. One important discrepancy to be aware of is that what is labeled Hwy 21 east of Santa Rosa is labeled as CA-11 when you zoom in. On my extensive paper map, this road appears only as CA-11 (a name that it keeps continuing on to Honduras and Copán Ruinas). This road is about mid-way between San Esteban and Santa Elena and goes east/northeast.
To say that Google Maps only has a little bit of information on the Department of Petén would be a gross overstatement. It has virtually nothing. Looking at Google Maps, you would think that there were no roads in this department at all. On the contrary, in addition to the road around Lago Petén Itzá, also home of the famous Mayan ruins of Tikal, Flores has three major highways going out from it: Hwy 5 going south to Alta Verapaz, which leads to many Mexican border crossings, southeast to the southwestern tip of Belize and to Izabal and Río Dulce, and an eastern route that crosses into Belize at Ciudad Melchor de Mencos. You can reach some of northern Petén by road, but the abundance of airports indicates that perhaps travel might be difficult by road. Google Maps does not do justice to what is referred to as "the cradle of Mayan civilization."
Major Cities: Flores, Ciudad Melchor de Mencos and Frontera Echeverria, Poptún
El Progreso, bordering the department of Guatemala, is represented pretty well on Google Maps. CA-9 and Hwy 17, the major highways in this department, are well-marked. Some smaller roads that go to towns a bit off the beaten path are not numbered, but they are clearly drawn. The Google Map of El Progreso is one of the better maps of departments and give you a good sense of locations for planning purposes.
Major Cities: El Progreso, San Agustín Acasaguastlán, Sanarate
The Department of Quiché has most of its major road adequately represented - from Hwy 15 that comes up from CA-1 to Hwy 5 that goes from Huehuetenango to Coban (which I hear is a beautiful, but challenging, trip!) What's really odd, though, is though Chichicastenango, a large city, is marked on the map, the capital of the department, Santa Cruz del Quiché, is not marked at all. This route is a common tourist route, so you'd think it would be included. Another city on this route that is missing is Sacapulas, which is the town at the crossing of 7W/CA-5 and Hwy 15. This is an important town, especially if you're taking a bus in Guatemala. Less important to know is that Hwy 15 continues north to Chajul - you can't see that road on this map, though you can see Chajul. Some important elements are missing in this Google Map, so I wouldn't depend on it.
Major Cities: Santa Cruz del Quiché, Chichicastenango, Sacapulas
The Google Map of the department of Escuintla is pretty good, like the other departments that are close to the capital. Most of the major roads are covered (CA-9, CA-2) as well as the highway south from Escuintla to Puerto Quetzal. Many minor roads that branch off south of CA-2 west of the city of Escuintla show up as gray lines as you zoom in, but are not all labeled. Another larger town that is in the department of Escuintla that is not on Google Maps is Palin, about 10-15 kms before you reach the border of Escuintla department going toward Amatitlán on CA-9. Overall, this map is useful for planning and some off the major highways with some decent Spanish to ask directions.
Major Cities: Escuintla, Puerto Quetzal, Palin, Puerto San José