Upgrade from Aperture on Mountain Lion to Photos on Yosemite

Back up everything first, upgrade the OS, click here, and follow the instructions.

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Just be very aware that Photos is a much less capable application than Aperture. It's much closer to iPhoto in features than Aperture. It's not an upgrade.

I'm afraid I could lose my Geo-Tag-Infos – is this possible?

(This would be a disaster!)

The migration to Photos will preserve the location data, the face, titles and captions. See this document:

How Photos handles content and metadata from iPhoto and Aperture - Apple Support

How Aperture content and metadata migrate to Photos

Photos and organization:

• Photos and movies migrate without changes. Photos migrate with the adjustments and filters you applied in Aperture. You can't modify the adjustments in Photos, but you can revert to the original image.
• Projects and subfolders migrate to a folder labeled “Aperture Projects" and a folder labeled "iPhoto Events" in the Albums view.
• Albums are preserved in Photos.
• Most Smart Albums are preserved in Photos. Smart Albums with selection criteria that isn’t supported by Photos usually migrate to Smart Albums with "(modified)" added to the Smart Album name; in cases where none of the Smart Album criteria are supported in Photos, the Smart Album isn't migrated.
• Photo books migrate to Albums.
• Slideshows are preserved in Photos. If a slideshow's theme is not available in Photos, it uses Photo's default slideshow theme.

Keywords and other metadata:

• Keywords are preserved in Photos.
• Photos preserves user-defined titles. Images without user-defined titles will show as "untitled" in Photos.
• Star ratings migrate as similar keywords in Photos, such as “1 Star,” “2 Stars,” and so on.
• Flagged images migrate with the keyword “Flagged” and appear in the “Flagged” Smart Album in the Albums view.
• Color labels migrate as keywords, such as “Green” and "Purple.”
• Captions are preserved in Photos.
• Most metadata is preserved in Photos. Some IPTC metadata, including Copyright, won't appear in Photos, but is still associated with the image and can be seen in iPhoto, Aperture, and other applications that display IPTC metadata.
• Custom metadata fields don't migrate to Photos.

This user tip mentions a few precautions you might take before migrating to Photos: Notes on Migrating an Aperture Library from Aperture to Photos for Mac