Cesium baseImage change production tool

I want to change the default BaseMap.

However, the location on the map goes up, so it doesn’t fit the South Korean location.

Is there any authoring tool to create baseMap offline?

You are looking for related material.

Would you share more about what you are trying to do? Do you want all of South Korea to be a certain color?

QGIS is a free program for viewing, creating, and editing geospatial data. I would create a geotiff raster in QGIS for this purpose, and then upload it to Cesium Ion. QGIS has some good documentation and tutorials to get started.