For me, the ideal city would be like the city of Amesterdam. This is because in Amsterdam there is a good availability of public transport such as the metro or tram, and above all, there is a good bike path that covers the whole city and surroundings.
However, the factor that makes this city an example for others is the mentality of people, who are more likely to use public transportation or to ride a bike rather than take the car.
In addition the city as much of the nation is powered by clean energy, produced by wind energy and hydroelectric energy.

I agree with you, but I have to say that Amsterdam is not the only city that is ecological. For example, also Copenhagen is a very green city (according to the Global Green Economy Index 2016, Copenhagen is the most ecological city in all the earth planet). In fact: the public transport system is well developed, the cars are few and every day more than 1 million km are traveled by bike; one food store in ten sells organic food; It is also an example for sustainable construction, as confirmed by the complex of Orestad City, a few kilometers from the capital, built in less than a decade.
I think that more cities like Amsterdam or Copenhagen will be the next future if the Humanity really want to survive and "save" the planet. But is correct to say that kind of cities like that are possible because of the morphology of the territory and because of the open mind of the population of the cities.

I'm not totally agree with you, because even cities that have gradients if they want and if they are incentivized to change would be able to find a solution to be more environmentally friendly. For example, they could increase parking prices and reduce their number so as to encourage people to use public transport, or they could make electric bikes available.