Previously I recommended historical GIS resources include:

Recently discovered OldMapsOnline - a globally-oriented historical mapping solution.

Overview

Free open-access platform aggregating 500,000+ high-res historical maps (16th-21st c.) from institutions including:
• British Library
• Harvard Library
• David Rumsey Map Collection
Volunteer-powered expansion supports researchers/educators.

Official site: https://www.oldmapsonline.org/
Operational differences from AllHistory yield distinct features.

Core Asset: Historical Map Repository

• Global coverage from elite archives
• Region-specific discovery (e.g. Shandong Province):

• Georeferenced maps support overlay analysis

Global Timeline

Synchronized visualization of dynasties/rulers/events worldwide:

Historical Entities

• Figures/events sourced directly from Wikipedia
• Less curated than AllHistory's structured data:


Mainland users: Access may require workarounds

Platform Comparison

Feature OldMapsOnline AllHistory
Map Archive ★★★★★ (Core strength) ★★★☆☆
Timeline Function ★★★★☆ (Global synchronization) ★★★★☆
Data Quality ★★☆☆☆ (Raw Wikipedia feeds) ★★★★☆ (Curated datasets)
Operations Community-driven Corporate-managed

Critical Note: Inaccurate PRC post-1949 borders - persistent issue in foreign platforms.

Contribute your historical GIS resources below!