How To Date An Undated World Map

Created by Randall Munroe at XKCD as Map Age Guide, click for larger versionThe flowchart above is a classic from Randall Munroe at XKCD showing how you can relatively easily figure out the date of any undated world map (assuming it’s complete, in English and has enough details).

And if you want to know read the full text see below (provided by Explain XKCD):

• Going through the flowchart, taking the leftmost path first, recursively. (Note there is no recursive loop, any loop is your mistake). See also Depth-first search.
  • “Prior Date Range” is the range determined immediately before the question, carried over from the previous question.
  • “Question Date Range” is the range each answer choice implies.
  • “New Date Range” is the intersection of the Prior Date Range and the Question Date Range for each choice, and is the range determined by all questions hitherto answered.

#	Question	Prior Date Range	Question Date Range	New Date Range
1	Istanbul or Constantinople	Start here	Constantinople: 330 – 1928	Constantinople: 330 – 1928 (Go to 2)
			Neither: inconclusive	Neither: inconclusive (Go to 19)
			Istanbul: 1928+	Istanbul: 1928+ (Go to 51)
Note: the chart splits here into three divisions, each from a choice in question 1. The Neither Division will attempt to use other indicators to sort maps into one of the other two divisions or branches thereof; or, after 5 failures to find a country, conclude that the "map" in question is not a political map and proceed to find out what it is (the Not a Political Map Branch). The Constantinople and Istanbul Divisions are linear except where the Neither Division joins them as stated above.
Constantinople Division
2	Do any of these exist?	330–1928 (from 1)	No: 1867-	No: 330–1867 (Go to 3)
	Independent Canada	1299–1922 (from 19 in the Neither Division) (from 24 in the Neither Division)	Yes: 1868+	Yes: 1868–1928 (Go to 11)
	US Territory of Alaska
	Tokyo
Holy Roman Empire Branch
3	The Holy Roman Empire?	330–1867	Yes: 899–1806	Yes: 899–1806 (Stated in comic as "1805 or earlier," since modern map-making was fuzzy as a concept prior) (Stop)
			No: 899- or 1806+	No: 330–899 or 1806–67 (Go to 4)
4	The United States?	330–899 or 1806–67	No: 1776-	No: 330–899 (Not stated in comic, since a map in this period is probably not in English, which violates a proviso of the comic) (Stop)
			Yes: 1776+	Yes: 1806–67 (Go to 5)
5	Texas is...	1806–67	Part of Mexico: 1718–1836	Part of Mexico: 1806–36 (Go to 6)
	Part of Mexico?		Independent: 1836–46	Independent: 1836–46 (stated in comic as 1834–45 – a discrepancy) (Stop)
	Independent?		Part of the US: 1846+	Part of the US: 1846–67 (Go to 9)
	Part of the US?
6	Florida is part of...	1806–36	Spain: 1565–1763 or 1783–1821	Spain: 1806–21 (Go to 7)
	Spain?		The US: 1821+	The US: 1821–36 (Go to 8)
	The US?
7	Paraguay?	1806–21	No: 1811-	No: 1806–11 (stated in comic as 1806–10) (Stop)
			Yes: 1811+	Yes: 1811–21 (stated in comic as 1811–17 – a discrepancy (see question 6)) (Stop)
8	Venezuela and/or Ecuador?	1821–36	No: 1830-	No: 1821–30 (stated in comic as 1818–29 – a discrepancy (see question 6)) (Stop)
			Yes: 1830+	Yes: 1830–36 (stated in comic as 1830–33 – a discrepancy (see question 5)) (Stop)
9	Does Russia border the Sea of Japan?	1846–67	No: 1858-	No: 1846–58 (Go to 10)
			Yes: 1858+	Yes: 1858–67 (Stop)
10	The US's southern border looks...	1846–58	Weird: 1854-	Weird: 1846–54 (stated in comic as 1846–53) (Stop)
			Normal: 1854+	Normal: 1854–58 (stated in comic as 1854–56 – a discrepancy (where is 1857?)) (Stop)
South Africa Branch
11	South Africa?	1868–1928	No: 1910-	No: 1868–1910 (Go to 12)
			Yes: 1910+	Yes: 1910–28 (Go to 16)
12	Rhodesia?	1868–1910	No: 1895-	No: 1868–95 (Go to 13)
			Yes: 1895+	Yes: 1895–1910 (Go to 15)
13	Is Bolivia landlocked?	1868–95	No: 1825–84	No: 1868–84 (Go to 14)
			Yes: 1884+	Yes: 1884–95 (Stop)
14	"Buda" and "Pest" or "Budapest"?	1868–84	Buda and Pest: 1247–1873	Buda and Pest: 1868–73 (stated in comic as 1868–72) (Stop)
			Budapest: 1873+	Budapest: 1873–84 (stated in comic as 1873–83) (Stop)
15	Is Norway part of Sweden?	1895–1910	Yes: 1814–1905	Yes: 1895–1905 (Stated in comic as 1896–1905) (Stop)
			No: 1814- or 1905+	No: 1905–10 (Stated in comic as 1906–09) (Stop)
16	Austria-Hungary?	1910–28	Yes: 1867–1918	Yes: 1910–18 (Go to 17)
			No: 1918+	No: 1918–28 (Go to 18)
17	Albania?	1910–18	No: 1912-	No: 1910–12 (Stop)
			Yes: 1912+	Yes: 1912–18 (stated in comic as 1913–18) (Stop)
18	Leningrad?	1918–28	No: 1924- or 1991+	No: 1918–24 (stated in comic as 1919–23) (Stop)
			Yes: 1924–91	Yes: 1924–28 (stated in comic as 1924–29) (Stop)
Neither Division
19	Does the Ottoman Empire exist?	Inconclusive	Yes: 1299–1922	Yes: 1299–1922 (Go to 2 in the Constantinople Division)
			No: 1299- or 1922+	No: 1299- or 1922+ (Go to 20)
20	The Soviet Union?	1299- or 1922+	Yes: 1922–91	Yes: 1922–91 (Go to 21)
			No: 1922- or 1991+	No: 1299- or 1922 (November 1–December 28) or 1991+ (Go to 22)
21	Saudi Arabia?	1922–91	Yes: 1932+	Yes: 1932–91 (Go to 52 in the Istanbul Division)
			No: 1932-	No: 1922–32 (Stop)
22	North Korea?	1299- or 1922 (November 1–December 28) or 1991+	Yes: 1945+	Yes: 1991+ (Go to 69 in the Istanbul Division)
			No: 1945-	No: 1299- or 1922 (November 1–December 28) (Go to 23)
23	Saint Trimble's Island	1299- or 1922 (November 1–December 28)	No: inconclusive	No: 1299- or 1922 (November 1–December 28) (Go to 24)
			Yes: impossible	Yes: impossible (Stop)
24	Is Jan Mayen part of the kingdom of Norway?	1299- or 1922 (November 1–December 28)	Not yet: prior to 1930	Not yet: (Go to 2 in the Constantinople Division)
			What?: Not a political map	What?: (Go to 25)
			Yes: 1930+	Yes: (Go to 53 in the Istanbul Division)
Not a Political Map Branch
25	Can you see the familiar continents?		Yes: map of the Earth	Yes: map of the Earth (Go to 26)
			No: not a map of the Earth	No: not a map of the Earth (Go to 32)
Topographical Map / Satellite Image Subbranch
26	This sounds like a physical map or satellite photo.	Map of the Earth	Yes, that's it: topographical map or satellite image of the Earth	Yes, that's it: topographical map or satellite image of the Earth (Go to 27)
27	Is Lake Chad missing?	Topographical map or satellite image of the Earth	No: 1970s-	No: 1970s- (Go to 28)
			Yes: 1970s+	Yes: 1970s+ (Go to 31)
28	How far east do the American prairies reach?	1970s-	Indiana: Before 1830	Indiana: Before 1830 (Stop)
			The Mississippi: 1830–1880s	The Mississippi: 1830–80s (Stop)
			Nebraska: 1860s–1910s	Nebraska: 1860s–1910s (Go to 29)
			What prairies?: 1920s+	What prairies?: 1920s–1970s (Go to 30)
29	Is there a big lake in the middle of Southern California? (created by mistake)	1860s–1910s	No: before 1905	No: 1860s–1900s (Stop)
			Yes: 1905+	Yes: 1910s (Stop)
30	Is there a big lake in the middle of Ghana? (created on purpose)	1920s–1970s	No: before 1960s	No: 1920s–50s (Stop)
			Yes: 1960s+	Yes: 1960s–70s (Stop)
31	Is the Aral Sea missing?	1970s+	No: 1990s-	No: 1970s-90s (Stop)
			Yes: 2000s+	Yes: 2000s+ (Stop)
Topograpical Map / Satellite Image Subbranch ends
Fictional Map / Non-Map Subbranch
32	Rivers "Sirion" or "Anduin"?	Not a map of the Earth	Yes: map of Middle-earth	Yes: map of Middle-earth (Go to 33)
			No: inconclusive	No: not a map of the Earth (Go to 37)
Middle-earth Subbranch
33	Mordor?	Map of Middle-earth	No: S.A. c. 1000-	No: S.A. c. 1000- (Go to 34)
			Yes: S.A. c. 1000+	Yes: S.A. c. 1000+ (Go to 35)
34	Beleriand?	S.A. c. 1000-	Yes: Y.S. 583 First Age-	Yes: Y.S. 583 First Age- (stated in comic as First Age) (Stop)
			No: Y.S. 583 First Age+	No: Y.S. 583 First Age–S.A. c. 1000 (stated in comic as early Second Age) (Stop)
35	Númenor?	S.A. c. 1000+	Yes: S.A. 1–3319	Yes: S.A. c. 1000–3319 (stated in comic as late Second Age) (Stop)
			No: First Age- or S.A. 3319+	No: S.A. 3319+ (Go to 36)
36	The forest east of the Misty Mountains is...	S.A. 3319+	Greenwood the Great: c. V.Y. 4620–T.A. 1050	Greenwood the Great: S.A. 3319–T.A. 1050 (stated in comic as early Third Age) (Stop)
			Mirkwood: T.A. 1050–3019–03–28	Mirkwood: T.A. 1050–3019–03–28 (stated in comic as Late Third Age) (Stop)
			The Wood of Greenleaves: T.A. 3019–03–28+	The Wood of Greenleaves: T.A. 3019–03–28+ (stated in comic as Fourth Age) (Stop)
Middle-earth Subbranch ends
37	Cair Paravel?	Not a map of the Earth	Yes: map of Narnia	Yes: map of Narnia (Go to 38)
			No: inconclusive	No: not a map of the Earth (Go to 42)
Narnia Subbranch
Note: This series contains seven books, whose original publication order does not match their chronological order. Specifically, The Magician's Nephew is earlier than The Lion, the Witch and the Wardrobe', and The Horse and His Boy is between The Lion, the Witch and the Wardrobe and Prince Caspian. Questions in this subbranch concern whether the place referenced can be found in the map contained in each book, not in which books' time the place exists. Therefore, places that exist in a book published later but is chronologically earlier than another book will not appear in the latter book, even if canonically they still exist in its time. Here are the seven books in their original publication order, which they will be referred to as.
1. The Lion, the Witch and the Wardrobe
2. Prince Caspian
3. The Voyage of the Dawn Treader
4. The Silver Chair
5. The Horse and His Boy
6. The Magician's Nephew
7. The Last Battle
38	Calormen?	Map of Narnia	No: 3-	No: 3- (Go to 39)
			Yes: 4+	Yes: 4+ (Go to 41)
39	Lotta islands?	3-	No: not 3	No: 2- (Go to 40)
			Yes: 3	Yes: 3 (Stop)
40	Beruna	2-	Ford: 1	Ford: 1 (Stop)
			Bridge: 2	Bridge: 2 (Stop)
41	Weird recursive heaven?	4+	No: 6-	No: 4–6 (stated in comic as one of the random later books) (Stop)
			Yes: 7	Yes: 7 (Stop)
Narnia Subbranch ends
42	Mossflower?	Not a map of the Earth	Yes: Redwall	Yes: Redwall (Stop)
			No: inconclusive	No: not a map of the Earth (Go to 43)
43	Is the world on the back of a turtle?	Not a map of the Earth	Yes: Discworld	Yes: Discworld (Stop)
			No: inconclusive	No: not a map of the Earth (Go to 44)
44	Are you sure this is a map?	Not a map of the Earth	Yes: a map for sure, just not of the Earth	Yes: a map for sure, just not of the Earth (Go to 45)
			No: not a map	No: not a map (Go to 47)
45	Did you make it yourself?	A map for sure, just not of the Earth	Yes: a homemade map	Yes: a homemade map (Go to 46)
46	It's very nice.	A homemade map	Thank you!: something "very nice"	Thank you!: a "very nice" homemade map (Stop)
Not a Map Subbranch
47	Is it trying to bite you?	Not a map	No: doesn't bite	No: doesn't bite and not a map (Go to 48)
			Yes: bites	Yes: bites (Go to 49)
48	Is it larger than a breadbox?	Doesn't bite and not a map	Yes: larger than a breadbox	Yes: larger than a breadbox, doesn't bite, and not a map (comic guesses a tuba) (Stop)
			No: smaller than a breadbox	No: smaller than a breadbox, doesn't bite, and not a map (comic guesses a stapler) (Stop)
			About the same: about the same size as a breadbox	About the same: about the same size as a breadbox, doesn't bite, and not a map (comic guesses a breadbox) (Stop)
49	If you let it go, what does it do?	Bites	Hisses and runs away: hisses and runs away if let go	Hisses and runs away: bites, and hisses and runs away if let go (comic guesses a cat) (Stop)
			Screeches and flaps around the room breaking things: screeches and flaps around the room breaking things if let go	Screeches and flaps around the room breaking things: bites, and screeches and flaps around the room breaking things if let go (comic guesses a seagull) (Stop (however, see 50))
50	Does the screeching chill your blood and herald death?	Bites, and screeches and flaps around the room breaking things if let go	Yes: Screeching chills your blood and heralds death	Yes: bites; screeches and flaps around the room breaking things if let go; screeching chills your blood and heralds death (title text guesses a banshee) (Stop)
			No: Screeching does not chill your blood and herald death; or does not screech	No: bites; screeches and flaps around the room breaking things if let go; screeching does not chill your blood and herald death (title text guesses a seagull) (Stop)
Istanbul Division
51	Does the Soviet Union exist?	1928+	Yes: 1928–1991	Yes: 1928–1991 (Go to 52)
			No: 1991+	No: 1991+ (Go to 69)
West Africa branch
52	Is most of West Africa a giant French blob?	1928–1991	Yes: 1928–1960	Yes: 1928–1960 (Go to 53)
			No: 1960–1991	No: 1960–1991 (Go to 60)
53	Pakistan?	1928–1960	No: 1928–1947	No: 1928–1947 (Go to 54)
			Yes: 1947–1960	Yes: 1948–1960 (Go to 56)
54	How many Germanys are there?	1928–1947	One: 1928–1940	One: 1928–1940 (Go to 55)
			One, but it's huge: 1941–1945	One, but it's huge: 1941–1945 (Stop)
			Two: 1946–1947	Two: 1946–1947 (Stop)
55	Persia or Iran?	1928–1940	Persia: 1930–1934	Persia: 1930–1934 (Stop)
			Iran: 1935–1940	Iran: 1935–1940 (Stop)
56	Cambodia?	1948–1960	No: 1948–1953	No: 1948–1953 (Go to 57)
			Yes: 1953–1960	Yes: 1953–1960 (Go to 59)
57	Eritrea is a part of...	1947–1953	Italy: 1948–1952	Italy: 1948–1952 (Go to 58)
			Ethiopia: 1952–1953	Ethiopia: 1952–1953 (Stop)
58	Canada is...	1947–1952	Missing a piece: 1948	Missing a piece: 1948 (Stop)
			Fine: 1949–1952	Fine: 1949–1952 (Go to 63)
59	The United Arab Republic?	1953–1960	No: 1953–1958	No: 1953–58 (stated in comic as 1954–57 – a discrepancy) (Stop)
			Yes: 1958–1960	Yes: 1958–60 (Stop)
60	How many Vietnams are there?	1960–1991	Two: 1960–1975	Two: 1960–1975 (Go to 61)
			One: 1975–1991	One: 1975–1991 (Go to 64)
61	Bangladesh?	1960–1975	No: 1960–1972	No: 1960–1972 (Go to 62)
			Yes: 1972–1975	Yes: 1972–1975 (Stop)
62	Is the area south of Lake Victoria...	1960–1972	British: 1960–1961	British: 1960 (Stop)
			Tanganyika: 1961–1964	Tanganyika: 1961–1964 (Stop)
			Tanzania: 1965–1971	Tanzania: 1965–1972 (stated in comic as 1964–1971 – a discrepancy) (Stop)
63	The town on I-25 between Albuquerque and El Paso is...	1949–1952	Hot Springs: 1916–49	Hot Springs: 1948–49 (Stop)
			Truth or Consequences: 1950+	Truth or Consequences: 1950–52 (Stop)
64	Jimmy Carter is...	1975–1991	Being attacked by a giant swimming rabbit: April 20, 1979	Being attacked by a giant swimming rabbit: April 20, 1979 (Stop)
			Fine: 1975–1991	Fine: 1975–1991 (Go to 65)
65	The Sinai is part of what country?	1975–1991	Israel: 1976–1979	Israel: 1976–1979 (missing 1975?) (Stop)
			Mostly Israel: 1980	Mostly Israel: 1980 (Stop)
			Mostly Egypt: 1981	Mostly Egypt: 1981 (Stop)
			Egypt: 1982–1991	Egypt: 1982–1991 (Go to 66)
66	What's the capital of Micronesia?	1982–1991	Kolonia: 1982–1988	Kolonia: 1982–1988 (Go to 67)
			Palikir: 1989–1991	Palikir: 1989–1991 (Go to 68)
67	Republic of the Upper Volta or Burkina Faso?	1982–1988	Upper Volta: 1982–1984	Upper Volta: 1982–1984 (Stop)
			Burkina Faso: 1985–1988	Burkina Faso: 1985–1988 (Stop)
68	(Number of Yemens) + (Number of Germanys) = ?	1989–1991	Four: 1989–early 1990	Four: 1989–early 1990 (Stop)
			Three: mid-1990	Three: mid-1990 (Stop)
			Two: late 1990–1991	Two: late 1990–1991 (Stop)
Post-Soviet branch
69	Zaire? or: "Hong Kong (UK)"	1991+	Yes: 1992–1996	Yes: 1992–1996 (Stop)
			No: 1996+	No: 1996+ (Go to 70)
70	Serbia and Montenegro are...	1996+	One country: 1996–2006	One country: 1996–2006 (Go to 71)
			Two countries: 2007+	Two countries: 2007+ (Go to 72)
71	East Timor?	1996–2006	No: 1997–2001	No: 1997–2001 (Stop)
			Yes: 2002–2006	Yes: 2002–2006 (Stop)
72	How many Sudans are there?	2006+	One: 2007–2011	One: 2007–2011 (Stop)
			Two: 2011+	Two: 2011+ (Go to 73)
73	Is Crimea disputed?	2011+	Yes: 2014+	Yes: 2014+ (Go to 74)
			No: 2012–2013	No: 2012–2013 (Stop)
74	"Colorado" or "Danger—Radioactive Exclusion Zone—Avoid"?	2014+	Colorado: 2014–2021	Colorado: 2014–2021 (Stop)
			Danger: 2022+	Danger: 2022+ (Go to 75)
75	Does the warning mention the spiders?	2022+	No: 2022	No: 2022 (Stop)
			Yes: 2023 or later	Yes: 2023 or later (Stop)

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• What If?
• What If? 2
• How To: Absurd Scientific Advice for Common Real-World Problems
• Thing Explainer: Complicated Stuff in Simple Words
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