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1. Initial Mapping Techniques and Tools

Ancient mapmakers relied on several tools and methods that assumed a flat Earth. Among these, the astrolabe was a crucial instrument for navigation and mapping.

Astrolabe

- Function: The astrolabe was used to measure the altitude of stars and celestial bodies above the horizon. It helped in determining latitude by measuring the angle between the horizon and a star, typically Polaris in the Northern Hemisphere.
- Flat Plane Assumption: The astrolabe operates on the principle that the Earth is flat. It measures angles and distances on a flat plane, and its calculations would be more complex and less accurate if the Earth were assumed to be spherical.

2. Creating the Azimuthal Equidistant Projection Map

The azimuthal equidistant projection involves creating a map that assumes a flat Earth with a central point. Here is a detailed breakdown:

- Central Point: Mapmakers selected a central point, often a known city or landmark, as the reference for all measurements.
- Distance and Angle Measurement: Using tools like the astrolabe, sextant, and compass, they measured the distances and angles to other locations from this central point.
- Plotting Points: These measurements were plotted on a flat surface, preserving the true distances and directions from the central point. The azimuthal equidistant projection is particularly useful for navigation because it maintains accurate distances from the center to any other point on the map.

3. Development of Detailed Flat Earth Maps

As exploration expanded, the details on flat Earth maps increased. These maps provided accurate representations of distances and directions based on terrestrial observations:

- Explorers and Traders: Information from explorers and traders helped to update and refine these maps. Their reports on distances, travel times, and directions were all based on the flat Earth assumption.
- Navigation and Trade: Flat Earth maps were essential for navigation and trade. Mariners used them along with their tools to find and follow routes, relying on the accuracy of the azimuthal equidistant projection.

4. Transformation to a Globe

When the spherical Earth theory became more widely accepted, cartographers faced the task of transforming their flat Earth maps into a spherical representation:

- Mathematical Adjustments: Using trigonometric and geometric methods, mapmakers developed techniques to project points from their flat maps onto a spherical surface. These calculations were complex but necessary to align the flat Earth data with the spherical model.
- Sectional Maps: Flat Earth maps were divided into sections that could be individually adjusted and then combined to form a globe. Each section was mathematically transformed to fit the curvature of a sphere.
- Constructing the Globe: These adjusted sections were pasted onto a spherical model to create a globe. This process relied entirely on the data from flat Earth maps, merely transformed to fit a spherical surface.

Flat Earth

The key argument is that the creation of the globe was fundamentally based on the initial flat Earth maps:

- Initial Data: The earliest detailed maps, created using the azimuthal equidistant projection, assumed a flat Earth. This was the foundational data for later globe-making.
- Tools and Methods: Tools like the astrolabe, which operate on the principle of a flat Earth, were essential for creating accurate maps. These tools would be less accurate or practical if the Earth were assumed to be spherical from the start.
- Transformation, Not Creation: The creation of globes was a process of transforming flat Earth maps into a spherical model, not creating new maps based on spherical observations. The original data and methods were rooted in the flat Earth assumption.