Usually determined by what the point of the graph is. If you are showing interest rates over last 10 years, 1 year may be a good interval. However if you just want to show a general rise over the 10 years, you may just have the two edge numbers and no intermediate values.
Similarly horizontal values. Eg if you are showing house prices change for a house bought for 245,000 in 1990, you may just show the value 245,000 as the prices rise and fall.
In general show the minimum bars needed to make your point.
A linear graph. As opposed to a logarithmic scale graph.
a bar graph
bar graph
a line plot
Intervals
line graph
They are called intervals.
The scale in a graph is determined by the range of the dependent and independent variables.
The answer depends on what the graph displays.
Intervals and units of measurement
Histogram
a histrogram