Updated text
I made a tutorial out of this answer and posted it on Wolfram Community. It's slightly different, and may be worth to check out.
Data from Wolfram Knowledgebase
The most straightforward way to plot data about counties is to use the built-in county entities and GeoRegionValuePlot.
counties = Cases[
EntityList@Entity["AdministrativeDivision", {"Country" -> Entity["Country", "UnitedStates"]}],
Entity[_, {_, _, _}] (* separates states from counties *)
];
GeoRegionValuePlot[counties -> "ForeignBornFraction"]
Here ForeignBornFraction is an entity property to adminstrative divisions.
Creating a US county entity store
Wouldn't it be nice if we could visualize our own data like this?
GeoRegionValuePlot[counties -> "CustomUnemploymentData"]
In the just released Mathematica 11 we can achieve that goal with entity stores. Since the built-in county entities don't have county FIPS codes and we need FIPS codes to correlate the entities with our data, I'll take the FIPS codes that JasonB shared in his answer, and make my own entity system.
fipsRules = Import["http://pastebin.com/raw/YSsKAbjn"]; (* JasonB's FIPS codes file, see his answer for details. *)
testdata = Rest@Import["https://gist.githubusercontent.com/mbostock/4060606/raw/25385f68a3be5c9dbe36af27fc2498fb2aab6bc0/unemployment.tsv", "TSV"];
getEntity[fipsRules_][{fips_, unemployment_}] :=
With[{entity = (IntegerString[fips] /. fipsRules)},
If[MatchQ[entity, _String],
Nothing, (* If the FIPS code does not exist in fipsRules *)
getEntityIdentifier[entity] -> <|
"Label" -> Style[entity["Name"], Bold],
"ParentEntity" -> entity,
"FIPSCode" -> fips,
"Unemployment" -> unemployment
|>
]]
getEntityIdentifier[Entity[_, {county_, state_, country___}]] := county <> "-" <> state
getEntityIdentifier[Entity[_, {"DistrictOfColumbia", _}]] := "DistrictOfColumbia"
countyEntities = Apply[Association, getEntity[fipsRules] /@ testdata];
So far we've imported both the unemployment data and the FIPS codes and used that to create an Association in the form dictated by EntityStore. Each entity in our custom entity store has the properties ParentEntity, FIPSCode and Unemployment. Label is also present, and is used for presentation.
ParentEntity is the built-in county entity and I will use that and computed properties to effect a sort of inheritance.
store = EntityStore["USCounty" -> <|
"Entities" -> countyEntities,
"Properties" -> <|
"ParentEntity" -> <|
"Label" -> "Parent entity"
|>,
"FIPSCode" -> <|
"Label" -> "County FIPS code"
|>,
"Polygon" -> <|
"DefaultFunction" -> (#["ParentEntity"]["Polygon"] &),
"Label" -> "Polygon"
|>,
"Position" -> <|
"DefaultFunction" -> (#["ParentEntity"]["Position"] &),
"Label" -> "Position"
|>,
"Latitude" -> <|
"DefaultFunction" -> (#["ParentEntity"]["Latitude"] &),
"Label" -> "Latitude"
|>,
"Longitude" -> <|
"DefaultFunction" -> (#["ParentEntity"]["Longitude"] &),
"Label" -> "Longitude"
|>,
"HasPolygon" -> <|
"DefaultFunction" -> (#["ParentEntity"]["HasPolygon"] &),
"Label" -> "Has polygon?"
|>,
"Name" -> <|
"DefaultFunction" -> (#["ParentEntity"]["Name"] &),
"Label" -> "Name"
|>
|>,
"EntityClasses" -> <|
"Alaska" -> <|
"Entities" -> ("ParentEntity" -> (MatchQ[#, Entity[_, {_, "Alaska", _}]] &)),
"Label" -> Style["Alaska", Bold]
|>,
"Hawaii" -> <|
"Entities" -> ("ParentEntity" -> (MatchQ[#, Entity[_, {_, "Hawaii", _}]] &)),
"Label" -> Style["Hawaii", Bold]
|>,
"Mainland" -> <|
"Entities" -> ("ParentEntity" -> (MatchQ[#, Entity[_, {_, Except["Alaska" | "Hawaii"], _}]] &)),
"Label" -> Style["Mainland", Bold]
|>
|>
|>];
The inheritance that I'm talking about is the properties that use DefaultFunction to compute their values. Besides the properties I also define three classes of counties, one for Alaska, one for Hawaii and one for the US mainland. The reason for this is that later I'll want to manipulate the three areas separately; I'll want to rescale and translate Alaska and Hawaii to the positions which they have in the map in the original post.
In order to be able to use the entity store you'll want to add it to $EntityStores:
AppendTo[$EntityStores, store]
I would also recommend adding as a resource object:
ro = ResourceObject[<|
"Name" -> "USCounty",
"ResourceType" -> "DataResource",
"Content" -> store
|>];
ResourceData[ro]; (* Needed to call this, otherwise the next line did not work. *)
ro["ResourceLocations"]
The advantage of this is that resource objects should be, I think, that they are persistent, i.e. next time you start up Mathematica you can get ahold of your data with
ResourceObject["USCounty"]
and add it to $EntityStores using
AppendTo[$EntityStores, ResourceObject["USCounty"]]
But right now this doesn't seem to work. It works within one session, but in a new session the resource object has disappeared. This feature as well is new in Mathematica 11. We can now do things like
EntityList["USCounty"] // Shallow
EntityList@EntityClass["USCounty", "Hawaii"]
Back to GeoRegionValuePlot
With the entity store in place we can now use GeoRegionValuePlot to plot our custom data like this:
GeoRegionValuePlot[EntityList[EntityClass["USCounty", "Mainland"]] -> "Unemployment"]
With a few options it looks almost the same as the image in the question:
getColor[val_] := Which[
0 < val < 0.01667, RGBColor[{247, 251, 255}/255],
0.0166 < val < 0.0333, RGBColor[{222, 235, 247}/255],
0.0333 < val < 0.05, RGBColor[{198, 219, 239}/255],
0.05 < val < 0.0666, RGBColor[{158, 202, 225}/255],
0.0666 < val < 0.0833, RGBColor[{107, 174, 214}/255],
0.0833 < val < 0.1, RGBColor[{66, 146, 198}/255],
0.1 < val < 0.1166, RGBColor[{33, 113, 181}/255],
0.1166 < val < 0.1333, RGBColor[{8, 81, 156}/255],
0.1333 < val < 0.15, RGBColor[{8, 48, 107}/255],
True, RGBColor[{8, 48, 107}/255]
]
GeoRegionValuePlot[
EntityList[EntityClass["USCounty", "Mainland"]] -> "Unemployment",
ColorFunction -> getColor,
ColorFunctionScaling -> False,
PlotLegends -> None,
PlotStyle -> Directive[EdgeForm[None]],
GeoBackground -> None,
GeoProjection -> {
"LambertAzimuthal",
"Centering" -> GeoPosition[{30, -195/2}]
},
PlotRange -> {{-0.37, 0.38}, {-0.13, 0.38}},
ImageSize -> 1000
]
The last details
The previous map still lacks the white borderlines, Hawaii, and Alaska. For Hawaii and Alaska we need to use Inset, so we have to use GeoGraphics. Hence, below is a GeoGraphics version of the previous plot.
getPolygon[entity_] := {
GeoStyling[None],
getColor[entity["Unemployment"]],
Polygon[entity]
}
alaska = GeoGraphics[
getPolygon /@ EntityList[EntityClass["USCounty", "Alaska"]],
GeoBackground -> None];
hawaii = GeoGraphics[
getPolygon /@ EntityList[EntityClass["USCounty", "Hawaii"]],
GeoBackground -> None];
map = GeoGraphics[{
getPolygon /@ EntityList[EntityClass["USCounty", "Mainland"]],
Inset[alaska, {-0.3, -0.06}, {0, 0}, 0.3],
Inset[hawaii, {-0.15, -0.06}, {0.1569, -0.0436}, 0.3]
},
GeoBackground -> None,
GeoProjection -> {
"LambertAzimuthal",
"Centering" -> GeoPosition[{30, -195/2}]
},
PlotRange -> {{-0.37, 0.38}, {-0.13, 0.38}},
ImageSize -> 1000
]
To add the borderlines I first make a black and white mask, where states are black and the background is white. The state borderlines that I want to draw are white as well; I then use ImageAdd to put the images together. The counties will be unaffected because we'll only be adding black to them, except for on the borderlines.
states = Cases[
EntityList@Entity["AdministrativeDivision", {"Country" -> Entity["Country", "UnitedStates"]}],
Entity[_, {_, _}]
];
alaska = GeoGraphics[
Polygon /@ EntityList[EntityClass["USCounty", "Alaska"]],
GeoBackground -> None];
hawaii = GeoGraphics[
Polygon /@ EntityList[EntityClass["USCounty", "Hawaii"]],
GeoBackground -> None];
borders = GeoGraphics[{
FaceForm[Black],
EdgeForm[White],
GeoStyling[None],
Polygon /@ states,
Inset[alaska, {-0.3, -0.06}, {0, 0}, 0.3],
Inset[hawaii, {-0.15, -0.06}, {0.1569, -0.0436}, 0.3]
},
GeoBackground -> None,
GeoProjection -> {
"LambertAzimuthal",
"Centering" -> GeoPosition[{30, -195/2}]
},
PlotRange -> {{-0.37, 0.38}, {-0.13, 0.38}},
ImageSize -> 1000
];
ImageAdd[map, borders]
