Using Maps in Research
How can maps help?
Maps are made for many reasons, and as a result, vary in content. Some maps made for general purposes may show roads, towns and cities, rivers and lakes, parks, and State and local boundaries. New and old maps often reveal changing place names, and they may also show changes in the boundaries of nations and their subdivisions. They rarely name individual landowners or residents.
In the United States, birth, death, property, and some other kinds of records are normally kept by county governments. If you can name the place where a kin lived, new or old maps of that place may also show the county seat where useful data about your kin may be obtained. Searches for data about an ancestor are often complicated by changes in the names and boundaries of places. GNIS The Geographic Names Information System (GNIS) is the Nation's official data base for place names. GNIS is maintained by the U.S. Geological Survey and can often provide information on name changes. This data base contains two million entries. They include the names of places that no longer exist as well as other or secondary names for existing places.
This automated system also contains the names of every type of feature except roads and highways. It is especially useful for genealogical research because it contains entries for very small and scattered communities as well as churches and cemeteries, including entries for those that no longer exist.
Complete listings or special searches, for example, for churches in a particular county, are available in high-quality bound listings or on magnetic media. There is a nominal charge for this service.
The boundaries of many political jurisdictions where early Americans lived have changed one or more times. some American families lived in the same locale for hundreds of years. Yet, the name of the place may have changed over time. Many counties have been subdivided several times, but family records were most often kept where they were originally filed.
This can greatly complicate your work. In one case, for example, the place where a family lived for the entire 19th century was over time part of seven different counties. In such a case, you might have to query all seven courthouses to obtain data needed about members of the family. Copies of records are rarely acquired by a succeeding county.
Similar, but even more complex problems arise when you must search for personal records in the archives of faraway lands. The names and boundaries of countries seem to be forever in flux and many public and private record centers disappear or move from place to place. 

Some places are hard to find. . . . Some have changed names one or more times. Some are too small to be shown on a map or noted in a gazetteer. And some are now ghost towns. Some of these places may be noted on an old map. The location of some others may be found in such sources as lists of abandoned post offices, local histories, government records, microfilm records or clippings from old newspapers, old city directories, or old county atlases kept in the library or archives of a town, city, or county in the region.
If you know the ward, district, neighborhood, or street of a city where an ancestor lived, an old map used in conjunction with a new map of the city may expedite your search for needed facts.
Books that show changes in county boundaries can help locate likely sources of records about relatives.
A librarian near where you live may be able to suggest someone who has access to such sources as Map Guide to the US Federal Census, 1790-1920: Genealogical Publishing Company, Baltimore, 1988.
This 445-page book shows all U.S. county boundaries from 1790 to 1920. On each of nearly 400 maps, old county lines are superimposed over modern ones to highlight boundary changes at 10 year intervals.
Separate books or papers have been published about the "genealogy" of each of a large number of States, counties, and other areas.
It will be worthwhile to gain access to modern and old maps of each ancestral site. You should try to find an old map that shows an area as it was close to the time your ancestor lived there.
National Gazetteer of the United States of America, Concise 1990, U.S. Geological Survey Professional Paper 1200-US: U.S. Government Printing Office, Washington, 1990. Directories of map collections Many libraries have the current edition of The Map Catalog: Vantage Press, a division of Random House, New York, 1990.
This handbook describes features and sources of a worldwide range of new and old maps, atlases, and related products. Has sections on researching old maps, history maps, maps of the United States and of foreign countries, State and provincial maps, county maps, urban maps and city plans, boundary maps, census maps, railroad maps, topographic maps, and many other kinds of maps.
Map Collection in the United States and Canada: A Directory: Special Libraries Association, New York, 1984, 4th ed.
Guide to U.S. Map Resources, 2nd Edition: American Library Association, Chicago, 1990.
Courtesy: U. S. Geological Survey

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on using maps in genealogical research
Some Types of Maps
Atlases A collection of maps in book form.

Sanborn Fire Insurance Maps One of the most valuable sources for monitoring and viewing urban change are the fire insurance maps published in the nineteenth century. These maps were drawn at the scale of 1 inch = 50 ft (later 1 inch =100 ft) which allowed very specific types of detail to be shown. For example, street width, building dimensions, the type of construction (frame, brick, stone), number of floors, roof composition, windows, elevators, wall construction, and street address are all shown. The fire insurance surveyors mapped the built-up area, central business district, and surrounding residential blocks for over 12,000 towns and cities nationwide by the 1950's. Their publication for urban areas continues today, and it is reported that every town in the United States with a population of 2,000 (in 1950) has been mapped. 

Gazetteers Gazetteers give the location (longitude and latitude, country, state, provience, etc.) of populated places and natural features. Some descriptive gazetteers also provide information about the population, economy, history, and industry of a given place.

Topographic Maps Topographic maps display relief features, water features, and cultural features. Large scale topographic maps, such as 1:24,000 scale maps are especially useful for areas where detailed information is needed. These maps will show detailed terrain and water features, major roads and power lines, cultural features such as schools, churches, cemeteries, dams, campsites, and mines.

Thematic Maps Thematic maps depict the distribution of a single attribute or the relationship among several. They cover such subjects as transportation and communication, political and historical geography, human and cultural geography, vegetation, water resources, agriculture, land use, public works, and regional or city planning maps.

Aerial Photography & Satellite Imagery Aerial Photography and satellite imagery refer to images taken, vertical or oblique, from an aircraft or orbiting satellite.

Road Maps Road maps show people how they can travel from one place to another. They also show some physical features, such as mountains and rivers, and political features, such as cities and towns. A road map also shows  which roads are main highways and which are smaller country roads.            

Plat Maps Drawing of a parcel of land--can include the name of the legal owner and the boundaries.

Articles & Aids for Maps, Deeds, & Land Records