How to Prepare a Large Map Image for Reliable Use in a Virtual Tabletop

Start by recording the map’s intended grid type, number of columns and rows, and whether the artwork has a grid drawn into it. For a square-grid battle map, choose a pixel size per square and multiply by the grid count. For example, a 30-column by 20-row map at 100 pixels per square is 3,000 × 2,000 pixels. The calculation gives you a target export size and makes it easier to spot accidental cropping or stretching.

Foundry’s guidance uses 100 pixels per square as a practical reference and recommends whole grid spaces, with the grid flush to the image edges. A background of 3,000 × 2,000 pixels at 100 pixels per square should therefore contain 30 columns and 20 rows. DPI/PPI metadata does not affect Foundry’s scene rendering. Foundry’s Content Creation Style Guide

If the map has a decorative border, blank margin, or partial squares, decide whether those belong in the playable area. A border can be useful visually, but partial squares at the edges make automatic grid matching harder. Keep the original art file so you can recrop or resize without degrading the only copy.

More pixels can preserve detail when players zoom in, but oversized images can take longer to transfer and may exceed a device’s rendering limits. Foundry reports that very large background dimensions can produce a black screen, with typical limits varying by hardware: around 8,000 pixels on older computers and 16,000 on newer ones. It recommends considering a lower export size such as 100 pixels per grid square. Treat those figures as cautions, not a guarantee that every device can handle a map just below them. Foundry’s scene-loading troubleshooting guide

Use the smallest export that still looks clear at the zoom your group needs. If players mainly view a battle map at normal scale, a 100-pixel grid may be adequate. If close zoom is important, test a higher-resolution copy on the least capable device in the group when possible. Roll20’s partner map guidelines recommend 140 pixels per square for square-grid map art, described as twice the 70-pixel grid cell scale, to reduce visible pixelation when zooming past 100%. These are platform-specific recommendations, not universal minimums. Roll20’s Map Art Guidelines

For a detailed map with painted textures, WebP can reduce file size while retaining reasonable visual quality. Foundry supports WebP and recommends it for its quality-to-size balance; its documentation also notes that WebP decoding uses more client processing. JPEG is another option for large, opaque artwork, but lossy compression can introduce visible artifacts. PNG preserves image data without lossy compression, though large scene backgrounds can become heavy to transfer. Compare exports at the zoom level players will use before choosing. Foundry’s Media Optimization Guide

Check the target platform’s accepted formats rather than assuming every VTT accepts the same files. Roll20’s tabletop overview lists JPG and PNG for images placed on the tabletop, while Foundry supports a broader set including WebP. A WebP file that is suitable for Foundry may therefore need a JPG or PNG export for Roll20. Roll20’s Tabletop Overview

For maps without a visible grid, preserve the intended dimensions and set the VTT’s grid to match. In Foundry, selecting a scene background automatically sets scene dimensions from the image; configure the grid size before adding walls, lights, tokens, or other positioned elements. Foundry notes that changing grid size later can shift those elements. Foundry’s Scenes guide

For a map with a pre-drawn grid, count the squares and divide the image width or height by the number of corresponding spaces. A 3,080-pixel-wide map with 22 columns works out to 140 pixels per column. Check the vertical calculation too: if width and height produce different pixel sizes per square, the image may be stretched, cropped, or use a non-square grid. Foundry provides a Grid Alignment Tool for fitting its overlay to a visible grid; Roll20 offers an Align to Grid tool for maps whose exact dimensions or crop are unclear. Foundry’s Scenes guide, Roll20’s Placing and Aligning Maps guide

Create a fresh scene or page for the map, upload the exported file, and make the scene or page dimensions match the image’s playable area. In Foundry, inspect the background path and image dimensions in scene configuration; if you override the dimensions, keep the image’s aspect ratio. Set grid type and size, then adjust alignment and offsets if a printed grid needs fine tuning. Foundry’s grid starts at the image’s top-left corner, so a margin before the first square may require alignment work.

In Roll20, upload the image to the Map layer, then use Page Settings and the image’s Set Dimensions option to match the intended units or pixel size. For a gridded map, its guide recommends aligning the map to the tabletop grid before trimming the page to the artwork. Hold Alt while moving or scaling there to bypass grid snapping. Once alignment is right, lock the map image’s position so a stray drag does not disrupt it. Roll20’s Placing and Aligning Maps guide

Check upload limits for your account before you prepare a very large file. Roll20’s map-alignment documentation lists a 10 MB per-asset limit for free users and 20 MB for Plus and Pro subscribers; limits can change, so consult the current platform documentation if an upload fails. If the file is over the applicable limit, reduce pixel dimensions or adjust compression, then inspect the new export for blur or compression artifacts.

Open the scene as a player or in a separate browser session if practical. Confirm that the image loads, that the full playable area is visible, and that tokens snap to the expected spaces. Compare several squares near the center and edges: a grid that aligns in one corner but drifts elsewhere may indicate the image was stretched or its grid is uneven. Zoom in on fine details and labels, then zoom out to check the overall view.

If the scene shows a black screen in Foundry, check whether the background image dimensions are too high for the hardware. A gray or blank background can also mean Foundry cannot find the configured image path. If it loads but the grid is off, correct the grid size or alignment before drawing walls or placing other scene details; those later elements depend on the scene geometry. For a more stable session, keep a lower-resolution export ready if the original proves slow or fails on a player’s device.

A reliable map is one whose export fits the target VTT, whose grid matches the art, and whose file loads and remains legible on the devices at the table. Record the final pixel dimensions and grid scale beside your map file so you can reproduce the setup if you move it to another scene or platform.

• Scenes — Foundry Virtual Tabletop

• Content Creation Style Guide — Foundry Virtual Tabletop

• Troubleshooting Scene Loading Issues — Foundry Virtual Tabletop

• Media Optimization Guide — Foundry Virtual Tabletop

• Tabletop Overview — Roll20 Help Center

• Map Art Guidelines — Roll20 Partners

• Placing and Aligning Maps — Roll20 Partners