Hexagonal grids
This guide will cover various ways to make hexagonal grids, the relationships between different approaches, and common formulas and algorithms. I've been collecting hex grid resources for over 25 years. I wrote this guide to the most elegant approaches that lead to the simplest code, starting from the guides by Charles Fu and Clark Verbrugge. Most parts of this page are interactive.
Hexagonal grids is a comprehensive guide from Amit Patel of Red Blob Games. It discusses multiple representations for storing hex grids, the trade-offs for each, and a list of common algorithms implemented in terms of grids.