The tax rate is one of the two factors (assessment value being the other) that when combined determine the actual amount of property taxes for any given property.
The assessed value is determined by the Municipal Property Assessment Corporation (MPAC), which is responsible for assessment services across the Province of Ontario.
The tax rate is set by the municipality so that when applied to the MPAC assessed value, enough tax revenue is generated to provide the approved services funded by the tax levy. Generally, affordable municipalites with low assessment values will require higher tax rates than municipalities whose properties are more expensive (higher assessment values).
When analysing whether there was an overall property tax increase or decrease, it is important to consider the changes to both the property assessment values and property tax rates. An increase in one of those factors can be offset by a decrease in the other factor. In fact, everything else being equal, they move in opposite directions.