I am trying to figure out the geographical extent of the 19 continental US timezones defined by tz. Because my goal is ultimately to create a freely available digital map, I would like to get definitions in terms existing, freely available digital maps, and the ones at nationalatlas.gov seem appropriate. Specifically, I plan to use countyp020 (county boundaries 2001), statesp020 (states) and timeznp020 (time zones) [see below for more details on those maps]. I tried to translate the comments in the "northamerica" file in terms of operations on the elements of those three maps, but I have a few questions/comments. 1. I would think that America/Boise, America/Denver and America/Phoenix together correspond exactly to the Mountain time zone of timeznp020. However, the later includes the southern quarter of Idaho County, Idaho, while northamerica suggests that this county is entirely in America/Pacific. Who is right? 2. The description of America/Denver includes "far eastern Oregon", and the description of America/Boise includes "eastern Oregon". Comparing with timeznp020, I suspect that America/Denver should not include "far eastern Oregon". (and if timeznp020 is right, "eastern Oregon" could be better described as "most of Malheur County, Oregon"). 3. What does America/Indiana/Indianapolis cover? Is it all the counties of Indiana not listed in any of the other zones? 4. The overall description of Indiana includes: # - Daviess, Dubois, Knox, Martin, Perry, and Pulaski counties # have been like America/Indiana/Vincennes. # # - Crawford, Pike, Starke, and Switzerland counties have their own time zone # histories as noted below. However, it seems that Pulaski now has it own zone (America/Indiana/Winamac), so it should probably be moved from the first to the second bullet in the quote above. 5. The description of America/Indiana/Marengo is that it covers the eastern part of Crawford County. How is that county divided, and in which zone does the western part fall? 6. What part of Kentucky goes in America/Kentucky/Louisville? At this point, I am not trying to handle border towns such as West Wendover, mostly because I have no idea of where to find a boundary for such towns. Any suggestion on what to do for those cases is welcome. For those of you who are curious about the content of the maps cited above: you can download them from <http://nationalatlas.gov/atlasftp.html> and visualize them using standard GIS tools (I use the freely available OpenJUMP and uDig). Alternatively, I have created a KML version of timeznp020 (using org2ogr) and placed it at <http://efele.net/timeznp020.zip> (4MB, 15MB uncompressed); you can visualize it in Google Earth (File->Open); I assume that the built-in 1st level and 2nd level admin regions (under "borders") are close enough to statesp020 and countyp020. Below is my current recipe to build my map in terms of operations in the source maps. Comments welcome. Thanks, Eric. --- Phoenix timeznp020/(Mountain & no DST) Boise statesp020/(Idaho+Oregon) intersected with timeznp020/Mountain North_Dakota/Center countyp020/(Oliver County, North Dakota) North_Dakota/New_Salem countyp020/(Morton County, North Dakota) Indiana/Marengo countyp020/(Crawford County, Indiana) // should only be the eastern part of Crawford County? where is the // limit? where does the western part go? Indiana/Vincennes countyp020/(Daviess, Dubois, Knox, Martin, and Perry Counties, Indiana) Indiana/Petersburg countyp020/(Pike County, Indiana) Indiana/Knox countyp020/(Starke County, Indiana) Indiana/Winamac countyp020/(Pulaski County, Indiana) Indiana/Vevay countyp020/(Switzerland County, Indiana) Kentucky/Louisville countyp020/(Clark, Floyd, and Harrison counties, Indiana) // what part of Kentucky is in this zone? Kentucky/Monticello countyp020/(Wayne County, Kentucky) Indiana/Indianapolis ? // statesp020/Indiana minus what is already covered above minus // Dearborn and Ohio County (they are in America/New_York) and // minus Gibson, Jasper, Lake, LaPorte, Newton, Porter, Posey, // Spencer, Vanderburgh, // and Warrick counties (they are in America/Chicago) Menominee countyp020/(Dickinson, Gogebic, Iron, and Menominee Counties, Michigan) Detroit statesp020/Michigan minus what is already covered above Los_Angeles timeznp020/Pacific minus what is already covered above Denver timeznp020/Mountain minus what is already covered above Chicago timeznp020/Central minus what is already covered above New_York timeznp020/Eastern minus what is already covered above ----