LONDON, Jan 7 (Reuters) - Global copper smelting activity was steady in December as a slowdown in China was offset by gains elsewhere, including other parts of Asia and North America, data from satellite surveillance of copper plants showed on Friday. Reduced activity in the southwest of China dragged down the overall performance in the world"s top refined copper producer, commodities broker Marex and SAVANT, a satellite analytics service it launched with Earth-i in 2019, said in a statement. But a rebound in other major producers of refined copper helped to steady global activity, they said. Power rationing in China last year led to a decline in the smelting activity, although this has since eased. Earth-i, which specialises in geospatial data, tracks more than 100 smelters representing 80% to 90% of global production. It sells data to fund managers, traders and miners and publishes a free monthly index of global copper smelter activity. Its global dispersion index was barely changed at an average of 51.6 in December compared with 51.7 in November. SAVANT launched the dispersion index in June, with 50 points indicating smelters are operating at the average level of the last 12 months. It also has a second index showing the percentage of active smelters. The China dispersion index fell to 53.5 in December from 57.4 in November, while a reading of the rest of world"s activity rose to 50.3 from 47.8 a month earlier. For 2021, global copper smelting activity in all measured regions recorded dispersion indices that were below 50. "That all regions recorded Activity Dispersion readings below the average of 50 for 2021, as a whole, should not necessarily be attributed to the global power crisis, with only South America experiencing noticeably weaker activity in the last quarter of the year," the statement said. There was little evidence so far to indicate that copper smelting was falling ahead of the Winter Olympics in China next month, the statement added.