> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/user-guide/2d-building/drawing/manage-underlays.md).
# Manage Underlays
An underlay is usually an architectural or mechanical plan, imported as a PNG file. You’ll trace over it to define thermal zones or spaces in the drawing area.
PNG works best as it keeps images sharp without losing detail. It’s ideal for clean lines, edges and transparency. If you have a PDF, convert it using your preferred software or a free tool like [pdf2png.com](https://pdf2png.com) for quick, high-quality results.
Keep your PNG under 1 MB. After importing, just calibrate and set a few preferences to start drawing. You’ll repeat the process for each zone and building level.
To be most useful, your underlay should show clear dimensions, orientation and all relevant areas.
## Import an Underlay
To import an underlay, click ‘Underlay’ in the drawing space ribbon, then press ‘+ Underlay’ and select your converted PNG file (ideally under 1 MB) from your local drive. Next, Click 'Add' to upload your inderlay.
## Delete an Underlay
To update an underlay, go to ‘Underlay’ in the drawing space ribbon and click the ‘x’ to delete the current one. Then, click ‘+ Add Underlay’ to upload a new PNG file from your local drive.
## Calibrate an Underlay
To calibrate an underlay, click ‘Calibrate Drawing’ in the drawing space ribbon. Left-click to mark the starting point, then hold and drag to the endpoint. Enter the known length and click ‘Calibrate’ to set the scale.
## Set Underlayer Opacity
To set underlayer opacity, go to ‘Underlay’ in the drawing space ribbon and navigate to Opacity. Then set the Opacity between 1 (xero opacity) and 0 (full Opacity).
## Rotate Underlay
To rotate underlay, go to ‘Underlay’ in the drawing space ribbon and navigate to Rotation. Then set the Rotation between -180 and + 180.
## Position an Underlay
To position an underlay, click ‘Position Underlay’ in the drawing space ribbon. Hold left-click and drag inside underlay to change its position. Hold left-click and drag underlay corners to change its size.
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