Side By Side Maps – Compare Historic and Modern Maps Online

Comparing historic and modern maps side by side has become significantly easier in recent years, thanks to free online tools that overlay or split-screen old cartography with current mapping data. For researchers, genealogists, and anyone curious about how a landscape has changed over time, these tools open a window into the past that was once only available in specialist libraries.

The most accessible options come from national libraries and mapping agencies, particularly in the United Kingdom, where organisations like the National Library of Scotland and Ordnance Survey have digitised vast collections. A third-party mapping resource describes the NLS geo explorer as “perhaps the best online free mapping application” for England, Scotland, and Wales.

Not all tools work the same way, and knowing which one to use depends on what you want to compare — historic maps, satellite imagery, or modern Ordnance Survey data. This guide covers the best free resources, how they work, and what limitations to expect.

What Is the Best Free Tool to View Side by Side Maps Old and New?

Quick Compare: Top Side by Side Map Tools

Key Insights About Side by Side Map Tools

• The National Library of Scotland (NLS) is the leading free resource for side by side historic-to-modern map comparison in the UK.
• Google Maps does not offer a native side by side old vs new map feature; dedicated georeferenced viewers are required.
• Georeferencing aligns old maps to modern coordinates, making side by side comparison accurate and usable.
• Most free side by side map tools focus on UK and Scotland coverage; global historic map options are more limited.
• OldMapsOnline provides access to over 500,000 high-resolution scanned maps from around the world, with a dedicated compare page.
• The NLS collection includes over a quarter of a million high-resolution images, with the strongest coverage in Scotland.
• Ordnance Survey has made historic maps from 1896–1904 available for side by side comparison with modern layers.

Key Facts: Side by Side Maps

How Do I Compare Old and New Maps Side by Side Online?

Using the National Library of Scotland Side by Side Viewer

The NLS side by side viewer is a free web application that lets you choose a historic map layer and compare it directly with a modern map. You can access it at maps.nls.uk/geo/explore/side-by-side/. Once open, the screen is split into two panels. The left panel displays the historic map, and the right panel shows a modern reference layer.

You can adjust which historic map is shown by selecting from the library’s collection of over a quarter of a million high-resolution images. The viewer also includes an overlay mode with a transparency slider and a Spy-glass viewer that lets you move a circular window over the modern map to reveal the historic layer beneath. According to Ordnance Survey, these three methods — overlay, split-screen, and spy-glass — are the main comparison modes used across most georeferenced map tools.

Using OldMapsOnline Compare

OldMapsOnline offers a dedicated Compare page with multiple comparison modes, including grid, swipe, and spy glass views. You can compare several maps at once, change their order, and use an opacity slider to control transparency. The service also includes a Georeference tool that lets you refine the overlay position, and users can upload their own scanned maps for comparison.

OldMapsOnline gives access to more than 500,000 high-resolution scanned maps from institutions worldwide. A timeline feature helps you browse maps by year, making it straightforward to track changes over decades. The Android app listing notes that users can “overlay a historical map on top of a modern map” to compare landscape and urban growth over time.

Using Ordnance Survey Layers and Guides

Ordnance Survey has published guidance showing how historic maps can be compared to present-day maps or satellite imagery once georeferenced. An OS GetOutside article highlights historical and modern Britain side by side using vintage OS maps from 1896–1904 and modern counterparts. OS also uses its Maps API Light Style as a grey backdrop mapping layer in its map search viewer, which can be combined with historic layers for comparison.

Can I View Side by Side Maps of the UK Using Google Maps?

Google Maps Does Not Offer Native Historic Map Comparison

Google Maps does not include a built-in feature for viewing historic maps side by side with modern ones. This is a common misconception. While Google Maps provides satellite and street-level imagery, it does not offer georeferenced historic map layers that can be toggled or compared in a split-screen view. For that, you need a dedicated tool like the NLS viewer or OldMapsOnline.

Google Earth as an Alternative for Historical Imagery

Google Earth does have a Historical Imagery feature that shows satellite and aerial photographs from different years. This is useful for seeing changes in land use, urban development, and natural features, but it is not the same as comparing historic cartographic maps. The imagery in Google Earth goes back to the mid-20th century at best, whereas tools like NLS provide maps from the 19th century and earlier.

Overlay vs Side by Side: Which Approach Works Best?

Both overlay and side by side modes have their strengths. Overlay mode with a transparency slider lets you fade between old and new maps directly on the same view, which can reveal subtle changes in boundaries and terrain. Side by side mode, by contrast, gives you an uncluttered view of each map in full detail, making it easier to compare road networks and place names. NLS and OS both note that split-screen side by side and overlay with transparency are the two most common comparison methods, and each tool typically offers both options.

What Is a Georeferenced Maps Viewer and Why Is It Accurate?

How Georeferencing Makes Comparison Possible

A georeferenced maps viewer takes an old scanned map and digitally warps it so that its coordinates align with modern mapping systems like those used by GPS and online maps. This process is called georeferencing. Without it, an old map would simply be a picture with no spatial relationship to the present-day landscape. Once georeferenced, the historic map can be overlaid or placed side by side with current maps, and features will line up with reasonable accuracy.

Accuracy Depends on the Original Map and Scanning Method

The accuracy of a georeferenced map varies. Historic maps were often drawn by hand and may contain distortions or inaccuracies that cannot be fully corrected. The scanning resolution, the quality of the original print, and the skill of the person doing the georeferencing all affect the final result. NLS and other institutions note that while georeferenced maps are useful for visual comparison and research, they are not perfectly accurate in a strict surveying sense.

Who Uses Georeferenced Map Viewers?

Researchers in urban planning, archaeology, environmental science, and genealogy use these tools to track changes over time. NLS notes that its viewers can be used to compare urban expansion, travel and communications, archaeology, woodland history, place names, and coastal erosion over a century or more. The University of Manchester Library also offers a Georeferencer tool for its Rylands collection, which is aimed at academic map research and allows users to view digitised maps side by side or as overlays on current mapping.

How Have Map Comparison Tools Evolved Over Time?

1. Pre-2010s: Physical map overlays used in research libraries. Comparing maps meant laying one paper sheet on top of another on a light table.
2. 2010–2015: Early georeferencing tools like Georeferencer launched by academic libraries, allowing digital alignment of scanned maps with modern coordinates.
3. 2015–2020: NLS launches its side by side viewer, and web-based split-screen tools become popular among historians and hobbyists. Open-source code is shared on GitHub.
4. 2020–2025: OS Maps API adds side by side layers, and OldMapsOnline expands its compare features with grid, swipe, and spy glass modes. Google Earth continues offering historical satellite imagery, but historic cartographic maps remain the domain of dedicated tools.

What Are the Common Misconceptions About Side by Side Maps?

Why Do Side by Side Maps Matter for Research and Planning?

Side by side maps are used to visualise urban development over time. By placing a map from the 1890s next to a current satellite view, researchers can see exactly how cities and towns have expanded, where railways were built or removed, and how industrial areas have been repurposed. This type of comparison is widely used in planning and historical conservation.

Environmental change is another major application. Coastline erosion, deforestation, and shifts in farmland boundaries become visible when old and new maps are aligned. For genealogists, seeing the landscape that ancestors would have known adds a layer of context to family history research. NLS notes that its viewers can be used to study place name changes, archaeological sites, and the history of woodland and travel routes over a century or more.

What Do Official Sources Say About Side by Side Maps?

“Compare georeferenced historic maps in a split-screen viewer side-by-side with other map layers.”

— National Library of Scotland, maps.nls.uk/geo/explore/side-by-side/

“The most obvious of these is using an overlay with a transparency slider, but it is also possible to use a split-screen Side-by-side viewer.”

— Ordnance Survey, Comparing Past to Present blog

“The Georeferencer tool can be used to view our digitised maps side by side or as overlays on current mapping.”

— University of Manchester Library, Rylands Georeferencer page

What’s Next for Side by Side Map Comparison?

Emerging trends in map comparison include AI-driven map alignment that automatically georeferences any uploaded old map, mobile side by side apps for field research and hiking, and integration of LiDAR data with historic maps to reveal vertical landscape change. Global digitisation projects from institutions such as the David Rumsey Map Collection and the British Library continue to expand the pool of available historic maps, making it easier to compare side by side across more regions and time periods. For a broader look at mapping tools, see the Map of North America – Countries, Terrain, Blank Maps Guide.

Frequently Asked Questions About Side by Side Maps