I explored this free map-based research tool a bit when it was first released by FamilySearch several years ago, but when chasing my husband's Powell ancestors around Bristol (figuratively!) I learned just how invaluable this free tool really is. The stars on the map to the left indicate the locations of the various parishes in which I found members of this family between 1807 and 1880.
English Jurisdictions 1851 is a free mapping and research tool created by FamilySearch and available at maps.familysearch.org. The Geographic Information System (GIS) visually displays parish maps of the 40 counties in England (not Wales, Scotland or Ireland, unfortunately) in Google Maps, accessible either by selecting a location on the map, or searching for a jurisdiction of interest. This isn't just a map, however -- it also simplifies research by consolidating data from many finding aids into a single searchable repository. More information about the sources that went into building this GIS can be found under the "Works Referenced" and "Glossary" tabs on the Help page.
England Jurisdictions 1851 is very easy to use. Just double-click to zoom in on the physical map or use the search box to drill down to your location of interest. If you are unable to locate a specific place of interest, then search for the next largest jurisdiction (city or county) and then select your parish or other location from the location list in the left-hand column. Zooming in and out on the map takes you from a general view of counties in England to a close-up view of parishes in a county.
Once you have narrowed your search, selecting a jurisdiction will bring up an information box, with details such as what type the place is (ancient parish, chapelry, ecclesiastical parish, etc.), plus the earliest available date of extant parish registers and/or Bishops' transcripts. Non-Church of England denominations in that locality are also identified. Selecting the Jurisdictions tab brings up a list of record-creating jurisdictions which have encompassed that specific locality (civil registration district, probate court, diocese, poor law union, hundred, etc.), important for locating records not kept at the parish level.
A third tab, identified as Options, includes some additional research tools and links. The one I find most helpful is a radius search for parishes within a range of 1/4 to 20 miles or km. The results are displayed as both a list of parishes with distances from the target parish, and on a Google map. This tool can help to determine which parishes are close enough by both mileage and terrain to be most worth including in a research plan. Other links take you directly to available information and/or records for the locality in the FamilySearch Wiki, FamilySearch Historical Records, and the Family History Library Catalog.
Speaking of terrain, with a parish or other locality highlighted, you can also use the map to easily view streets and terrain within the boundaries of your selected parish or other locality. The map here shows the location of "Cherry Lane" in St. James Parish, Bristol, where my husband's Powell ancestors lived for over a decade. Selecting "Map" in the upper-right corner will overlay the translucent parish outline over a Google street map, making it easy to correlate with census and other addresses. There are also links for satellite and Ordnance Survey maps.
If you have ancestors in England and haven't fully explored this free mapping research tool, now is the time. It is especially helpful for city research as demonstrated here, but can also be useful for rural parishes, both for identifying potential nearby parishes for research, as well as locating relevant record-keeping jurisdictions. Have fun exploring!