Русско-англо-русский юридический словарь

David Knowles: If it's a legal or formal text, stick with "oblast", possibly with an explanation. If it's less formal, go with "region". (ProZ)

Noginsk, city, Moscow oblast (region), western Russia, on the Klyazma River east of Moscow. (Britannica)

The entire Moscow region was put on an alert under a strict "counter-terrorist operation regime" ... (BBC)

"Field" is the specific subject that people study or an area of activity that they are involved in as part of their work. The individual is expected to know a great deal about the subject. Hence, the word "field" usually refers to an area of knowledge that is studied by scientists or by people studying it at a very high level, for example in a university. - Noel has a degree in Aerospace Engineering, but couldn't find a job in his field. (The Free Dictionary Forum)

The word "area" is usually used to imply an area of activity or responsibility. [...] NOTE: In certain sentences, there will be some overlapping in the choice of word. (The Free Dictionary Forum)

Ms Herndon is an expert in this field, and has a doctorate in music and computing from Stanford University in the US. (BBC)

This series is useful for teaching music lessons, particularly in the areas of music history, notation, composition, music theory and understanding styles. (BBC Teach)