Can debt to GDP ratio be reduced transfering debt to local autorities? It is my understanding that not only government but also local authorities issue bonds.
This answer on Money and Finance Stack Exchange suggests that such debts are not accounted in the computation of the government debt  (At least for the US). 

Questions:


Is there an estimate of the total municipal bond per countries?
Could a very indebted country try to reduce his debt to GDP ratio forcing local authorities to issue more bond and thus reducing the government spending? If yes, is there any country that attempted this strategy?
To answer your second question: a country could probably do that, but it would achieve not much more thereby than clean up that particular statistic. In Europe, the Treaty of Maastricht that specifies the maximum debt-to-gdp ratio a country can have pertains to the whole government sector, which is defined so as to include local authorities (see this explanation on the site of the Belgian government https://www.debtagency.be/en/datagovernmentdebtdebt). 

I don't know the situation in the U.S., but I think it can be assumed that in general any state or international institution that wants to know about another state's debt levels will not only look at the debt-to-gdp ratio.

In an analogous case, most E.U. officials are aware that the United States unemployment rate is on average lower than the European version partly because of differences in labour force participation, which works 'behind the scenes' of the official statistic (http://bruegel.org/2017/09/employment-in-europe-and-the-us-the-eus-remarkable-strength/).