Supporters of the Cumberland County Civic Center renovation project rolled out a very attractive picture of what the region’s publicly owned sports and entertainment venue would look like with a $33 million upgrade.

Taxpayers will be asked to approve bonds for the project, and for the first time got a good look at what they could expect to get for their money if the voters say “yes” on Nov. 8.

Equally compelling, if less attractive, is the picture of what would happen if they say “no.” The cost of doing nothing is not nothing, and voters will have to come to terms with the fact that an aging facility cannot accommodate popular traveling entertainers or hold on to the Portland Pirates minor league hockey team, the anchor tenant for the facility during what would otherwise be slow months in the winter.

Without the renovation, the civic center would become physically and economically obsolete, sucking the life out of downtown Portland during an already slow economy and turning a break-even or profit-making operation into a financial drag on taxpayers.

Neglect now would turn the civic center into a white elephant, more valuable as a tear-down than as a public asset.

Renderings released this week showed how the renovation would turn the 38-year-old arena into a place people would be excited to attend. Architects propose using glass walls to turn the idiosyncratic indented corners of the existing civic center into usable interior space that would provide more room for concessions.

A similar approach was recently used to reclaim wasted exterior space at the Monument Square main branch of the Portland Public Library. That renovation has turned what was becoming a shabby public property into an attractive and better-used public amenity that the whole community can be proud of.

The civic center’s supporters have to go a long way to sell a debt-averse electorate, at a time when the economic environment looks increasingly uncertain. They will have to make a strong case to convince voters that they can afford to make this investment now.

That means presenting two pictures. One that shows what the public would get by saying “yes,” and the other showing what would happen if it says “no.”