spec: add ternary-basic specification

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New Specification: ternary-basic

Closes #1001

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specification.md

ternary-basic: Basic Ternary Plot

Description

A ternary plot displays three-component compositional data on an equilateral triangle where each vertex represents 100% of one component. Points inside the triangle show compositions that sum to a constant total (usually 100%), with position indicating relative proportions. This visualization is essential for data where three variables are interdependent and constrained to sum to a fixed value.

Applications

• Analyzing chemical or material compositions (e.g., alloy mixtures, cement formulations)
• Soil classification using sand, silt, and clay proportions
• Visualizing market share distribution among three competitors
• Studying color mixing with RGB or other three-component systems

Data

• component_a (numeric) - Proportion of first component (0-100%)
• component_b (numeric) - Proportion of second component (0-100%)
• component_c (numeric) - Proportion of third component (0-100%)
• Size: 20-200 points work well; larger datasets may need density visualization
• Constraint: All three components must sum to 100% (or a constant total)

Notes

• Grid lines should be drawn at regular intervals (typically 10% or 20%)
• Each vertex should be clearly labeled with component names
• Points should be visually distinct with appropriate marker size and color
• Consider adding tick marks along each edge to aid reading proportions

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