How Our True Size Map Works: Methods & Calculations

This note explains the core ideas behind our true size map—why "map size" often differs from the real size, and how TrueSize.World exposes that gap without uploading any data.

Data & geometry

We use public boundary and coastline datasets optimized for web interaction (topology simplification, low-noise outlines). Precision cadastral work is out of scope; our focus is education and visualization.

Exaggeration by latitude (Web Mercator)

Many web maps use a Mercator-based projection. It preserves angles but inflates areas with latitude. A simple model of the linear scale factor is:

k(φ) = sec φ

At φ = 60°, k ≈ 2.0

At φ = 80°, k ≈ 5.8

We display a live center-latitude and an exaggeration ratio so users can relate what they see to a quantitative factor. When you drag Greenland toward the equator, its apparent map size converges toward its real size.

Overlays: opacity, rotation, alignment

Opacity lets you see two outlines simultaneously.

Rotation (with optional snaps) lets you align orientations and edges for apples-to-apples comparisons—great for the true size of islands or the real size of countries with similar silhouettes.

Basemaps & rendering

We provide standard, imagery, and terrain basemaps to fit different storytelling needs while keeping the interaction smooth.

Privacy & exports

Imports (GeoJSON) and drawings run locally in your browser. Exports—GeoJSON—are generated client-side. That's ideal for sensitive or unpublished geometries.

See also: Interactive Map