Order events across the B.C./A.D. and B.C.E./C.E. boundary, and explain how maps and globes reflect the perspective of the people who make them

Learning goal: Arrange events in order of occurrence using the conventions of B.C. and A.D. or B.C.E. and C.E., including events on both sides of the boundary between the eras, and explain how maps, globes and other geographic models reflect a certain perspective of people, places and environments, shaped by what geographers and cartographers decide to include and how they present it. This lesson teaches Ohio's 2026 social studies standards for Grade 6, published in July 2026. The Ohio Department of Education and Workforce anticipates that districts will begin implementing the 2026 standards in the 2027-28 school year.

Both halves of this lesson are about conventions: agreed ways of representing time and space. A convention is useful because many people share it, but it is also a choice, and every choice reflects someone's point of view.

Two labels, one numbering. Most of the world today numbers years from a starting point set in the 500s by a monk named Dionysius Exiguus, who counted from the year he calculated for the birth of Jesus. Years after that point are labeled A.D. (anno Domini, Latin for "in the year of the Lord"). Years before it are labeled B.C. ("before Christ"). Many historians and scientists now use C.E. ("Common Era") in place of A.D. and B.C.E. ("Before the Common Era") in place of B.C. The numbers are exactly the same: 221 B.C. and 221 B.C.E. are the same year. The newer labels exist because the older ones name a Christian belief, and people of many faiths use the same calendar. Choosing between the labels is itself an example of perspective.

Rules for ordering events.

1. Before the boundary, bigger numbers are earlier. B.C.E. years count down toward the boundary. 2560 B.C.E. is earlier than 221 B.C.E. because it is farther from the boundary.
2. After the boundary, bigger numbers are later. C.E. years count up. 622 C.E. is later than 105 C.E.
3. Every B.C.E. year is earlier than every C.E. year. 1 B.C.E. is earlier than 1 C.E.
4. There is no year zero. The year 1 B.C.E. is followed directly by 1 C.E. This matters when you calculate how long ago something was.

Calculating across the boundary. To find the number of years between a B.C.E. date and a C.E. date, add the two numbers and subtract 1, because there is no year zero. From 27 B.C.E. to 14 C.E.: 27 + 14 − 1 = 40 years. Within one era, subtract: from 2560 B.C.E. to 221 B.C.E. is 2560 − 221 = 2,339 years. Historians often round, but the rule is exact.

Centuries. The first century C.E. is the years 1 to 100. The fifth century B.C.E. is 500 to 401 B.C.E. A century's name is one more than the hundreds digit of most of its years, so the 1400s are the fifteenth century.

Maps reflect a perspective. A map, a globe or any geographic model is not a photograph of Earth. It is a representation made by people, and it reflects their perspective of people, places and environments: what they thought mattered, where they stood and whom they were making it for. Geographers and cartographers influence that perspective through at least five decisions:

- What goes in the center. Most maps used in Europe and the Americas place Europe and the Atlantic near the center. Many maps made in East Asia and Australia place the Pacific Ocean in the center. Each makes the maker's region look central.
- Which way is up. Putting north at the top is a convention, not a law of nature. The world map made by the geographer al-Idrisi for King Roger II of Sicily in 1154 placed south at the top, following a common practice of mapmakers in the Islamic world.
- Projection. A globe shows Earth's round shape, but every flat map must stretch or squeeze something. The Mercator projection of 1569 shows any route that keeps one constant compass bearing as a straight line, which helped sailors plot courses, but it enlarges lands far from the equator. On it, Greenland looks about as large as Africa, although Africa is about fourteen times larger.
- Names. Place names reflect who is naming. The terms "Near East," "Middle East" and "Far East" describe Asia by its distance from Europe. The Indian city of Bombay has been officially called Mumbai since 1995, a name drawn from a local goddess.
- What to include and leave out. A map of empires colors only the lands rulers claimed and may leave out the peoples who lived there. A map of trade routes may show merchants' paths but not the communities those routes passed.

Every map must leave things out, or it would be unreadable. The skill is to ask who made this map, for what purpose, and whose perspective does it show?

The misconception. Students often think a map is simply correct or incorrect. A map can be accurate and still reflect a perspective, because the choices of center, orientation, projection, names and content are all decisions someone made. Likewise, students sometimes think 100 B.C.E. is later than 50 B.C.E. because 100 is larger; in the B.C.E. era the larger number is earlier.

Worked example 1 — order events on both sides of the boundary: Order these events: Qin Shi Huang unifies China (221 B.C.E.); Muhammad's journey from Mecca to Medina, the hijra (622 C.E.); paper-making described at the Han court (traditionally dated 105 C.E.); the reign of Augustus begins as Rome's first emperor (27 B.C.E.); the Great Pyramid of Khufu is built (about 2560 B.C.E.). Solution: first place the B.C.E. dates, largest number first: 2560, 221, 27 B.C.E. Then the C.E. dates, smallest first: 105, 622 C.E. Order: pyramid, Qin unification, Augustus, paper, hijra.

Worked example 2 — calculate across the boundary: How many years passed between the unification of China in 221 B.C.E. and the hijra in 622 C.E.? Add and subtract 1 because there is no year zero: 221 + 622 − 1 = 842 years. Check with a smaller case: from 1 B.C.E. to 1 C.E. is 1 + 1 − 1 = 1 year, which matches the rule that 1 B.C.E. is followed directly by 1 C.E.

Worked example 3 — identify a map's perspective: A student compares two world maps. Map A uses the Mercator projection, puts Europe in the upper center and labels "the Far East." Map B is an equal-area map centered on the Pacific. Questions and answers: Where did Map A's maker place the center? Europe and the Atlantic, reflecting a European perspective. What does the projection do? It shows constant compass bearings as straight lines, which helps navigation, but it enlarges Greenland, Europe and northern Asia compared with Africa and South Asia near the equator. What does "Far East" tell us? That the maker described Asia by distance from Europe. Map B shows areas in true proportion and places the Pacific world at the center, a different perspective. Neither map is useless; each serves a purpose and reflects its makers' choices.

Timeline and map-audit task (representation): Draw a timeline from 3000 B.C.E. to 1000 C.E. with the boundary clearly marked and no year zero. Place at least six Eastern Hemisphere events with correct labels; use B.C.E./C.E. on the top edge and B.C./A.D. on the bottom edge for the same points to show the labels match. Then audit two world maps: record the center, the orientation, the projection (if stated), two place names and one thing each map leaves out.

Independent performance: Write a 200–300 word explanation titled "Whose time? Whose map?" Success criteria: (1) you order five events that span both eras correctly and explain the rule you used; (2) you calculate one interval across the boundary correctly, showing the no-year-zero step; (3) you explain why both B.C./A.D. and B.C.E./C.E. are used; (4) you describe at least three decisions a cartographer makes and how each reflects a perspective of people, places or environments; (5) you apply those decisions to one real map you examined and state its purpose and whose perspective it shows.