Atlas of Historical County Boundaries: Dataset

READ ME

---

How to Cite the [STATE NAME] File

Full citation information for a dataset can be found in the “Citation.PreferredStyle” in the Summary Metadata for each state. The Summary Metadata (ST_Metadata1.html) is located in the Supplemental Texts folder included with all the downloadable shapefiles. It may also be found at: www.newberry.org/ahcbp

Creative Commons License

The Newberry Library is the copyright holder.

These files are free for use under an Attribution-NonCommercial-ShareAlike Creative Commons License and may be downloaded from the Web site: www.newberry.org/ahcbp.

Organization of the Data

The data have been organized into folders containing sets of shapefiles and sets of supplementary information.

Historical Counties—a single shapefile that contains the polygons of every different, mappable version of each county—plus proposed (but unsuccessful) counties, extinct counties, and non-county areas—together with the corresponding attribute table and metadata, from the creation of the first county through 31 December 2000. All changes are dated to the day. The attribute table contains the county names, version numbers, FIPS codes, and the beginning and ending dates for each polygon, plus brief descriptions of the changes and citations to the sources for the changes.

Comprehensive Database—a tab-delimited text file which can be imported into the user’s preferred database program. The Comprehensive Database lists each change in each county, mappable or not. Like the attribute table for the Historical Counties shapefile, each entry in this datafile is limited to a single county (therefore, a given boundary change is reflected in entries for the two or more counties involved), but because non-mappable changes also are covered (e.g., a change in county organization or a boundary change too small to map, as in a shift from the center line of a road to a shoulder), this is a more comprehensive datafile and holds much more information than the attribute table. Most information is found in both the Comprehensive Database and the attribute table: the name, version number, and FIPS code for each county, start and end dates (dated to the day, month and year), a description of each change, and a citation to the authority for the change.

Supplemental Texts—a set of HTML files that provide information meant to increase the convenience and efficiency of the user’s work with the shapefiles and datafiles. Names in the Index are hyperlinked to the corresponding entries in the Individual County Chronologies.

• Index of Counties and Equivalents: an alphabetical listing by name of all counties, including extinct counties, with cross-references between names that have been changed.

• Consolidated Chronology: a single chronology of all changes in the state and county boundaries and names, organization, and attachments. Each entry describes the change (e.g., ALAMEDA created from CONTRA COSTA and SANTA CLARA) and gives the primary source(s) of the information (e.g., Calif. Stats. 1853, 4th sess., ch. 41/pp. 56-59). The organization of this document is chronological.

• Individual County Chronologies: a set of chronologies, each one covering all the changes in a single county or county equivalent, that describe the changes and give the primary source(s) of the information. These chronologies are organized, first, in alphabetical order by present-county name and then chronologically under each county.

• Bibliography and Sources: an alphabetical list of the primary and secondary sources found useful in the historical research and compilation of the evolution of the state’s county and state boundaries.

• Commentary: a description of the research problems or materials that were unusual or stood out in the research and compilation of the historical state and county lines and how the compiler handled them. [Note: A Commentary has not been written for every state]

• Metadata - Summary Form: a single-page document providing information about the data available on the website in text and maps. Includes: Project Description, Preferred Style for Citation, and Spatial Reference Information.

• Metadata – Full FGDC Form: a multi-page document containing comprehensive descriptions of The Atlas of Historical County Boundaries Project, the process used to compile and digitize the historical boundaries, and the following data and spatial information:

Identification_Information

Data_Quality_Information

Spatial_Data_Organization_Information

Spatial_Reference_Information

Entity_and_Attribute_Information

Distribution_Information

Metadata_Reference_Information

---

How to use the Historical Counties master shapefile to create a county boundary shapefile as of a selected date.

The Historical Counties master shapefile contains separate polygons for each unique county shape during the state's history. Due to the numerous changes that have occurred in county boundaries, the master shapefile includes many overlapping polygons. Each polygon includes field values specifying the start and end dates for that particular shape.

In some states (like California) there were changes which were too small to map as polygons. Such changes are symbolized as points and located in the folder named “Small_Changes”.The point files were digitized according to the year in which the small change took place (i.e. 1897_pt.shp). When viewed with the historical counties layer the dot on the related boundaries indicates the approximate location of the change too small to map as a polygon.

[Note: All shapefiles are initially set as “Read-Only” to prevent inadvertent editing. This can be changed in the Properties dialogue box for each folder.]

Using ESRI’s ArcMap software, it is simple to create a state map by county as of any selected date. This is done by entering an ArcMap definition query to restrict the master shapefile to only those county shapes in effect at your date. The shapefile can then be viewed and queried, or it can be exported to a separate shapefile or feature class for use in other applications. The procedure is as follows:

1. Bring the Historical Counties polygon shapefile into the ArcMap Table of Contents.

Launch ArcMap.

Click on the Add Data icon in the standard toolbar to open the Add Data dialog box.

Navigate to the master polygon shapefile and add it to the map.

2. Enter a Definition Query to display the county boundaries as of a specific date.

Double-click on the master polygon layer in the ArcMap table of contents to open the Layer Properties dialog box.

Select the Definition Query tab.

Click on the Query Builder button.

Enter (or Copy/Paste) the following text into the white box in the bottom of the Query Builder dialog. This particular query will display the county boundaries as of 12/31/1900. You can replace both instances of "19001231" with your date in YYYYMMDD format.

"START_N" <= 19001231 AND "END_N" >= 19001231

Click Verify to test whether the syntax is correct. If you receive an error message, check that this query text was entered correctly.

Click Save if you want to save this definition query for future use.

Click OK, then OK again for the query to go into effect.

The master polygon layer will now display county boundaries as of 12/31/1900.

3. Create a shapefile or Feature class of the county boundaries as of a specific date.

In the ArcMap table of contents, right-click on the Master polygon layer (which should contain the above definition query).

Select Data > Export Data to open the Export Data dialog box.

Select the "Export: All features" option.

Click on the Browse button. The Saving Data dialog box will appear.

To export the data as a shapefile:

Set the "Save as type" equal to "Shapefile"

Navigate to a directory and click Save.

To export the data as a feature class:

Set the "Save as type" equal to "Personal Geodatabase feature classes" or "SDE feature classes".

Navigate to an existing geodatabase and click Save.

Click OK to export the data.

The exported data will include only those features from the Master polygon shapefile that satisfy the definition query.