Even in the age of satellite mapping, determining just how much of Maine’s coast is accessible to the public is not an easy statistic to nail down.

A group of people working under the leadership of the state Department of Conservation to craft a consensus plan for the use of state-owned Sears Island in Searsport raised the question of accessible coastline. The issue was researched by the State Planning Office.

In meetings, some who advocate preserving the island have argued that Maine has just 25 miles of accessible coastline and that Sears Island represents 5 miles of that.

Not so, said Janet Parker, coordinator of geographic information systems for the planning office.

In fact, publicly owned shoreline measures at least 890 miles, Parker concluded.

Those who have used the 25-mile statistic are likely confusing a much-quoted figure that came out of the effort to preserve the state’s working waterfronts. Those leading the initiative found that just 25 miles of the coast could be used by fishermen for parking their vehicles, unloading bait and loading their catch, or loading and unloading their vessels.

Parker’s report on the shoreline question was forwarded by e-mail to those participating in the Sears Island planning process.

The calculations, she noted, were done quickly and likely do not include land held by land trusts, private individuals who allow public access, and waterfront land owned by municipalities.

Using a database, Parker computed the 890-mile figure by including state parks, state historic sites, state wildlife management areas, national or federal parks and preserves, some privately owned conserved lands and a few municipal conserved lands.

The planning office computes the state’s shoreline at 5,412 miles, a figure that includes islands and tidal estuaries. By that criteria, Parker said, both shores of the Kennebec River from the ocean to Augusta would be counted as shoreline.

Even offshore islands that are not much more than a pile of rocks are counted in the survey, she said.

Parker’s report assumes that all of the coastal “conserved lands,” as she refers to them, provide public access to the shore.

“Certainly any of the state lands would allow access,” she said Tuesday.

And she emphasized that the 890-mile figure is probably a low estimate.

But Scott Dickerson, executive director of the Camden-based Coastal Mountains Land Trust and a member of the Sears Island steering committee, said more context is needed for the statistics to be useful.

“What’s the definition of publicly accessible coastline?” he asked.

Access could be defined as a place where a boat can be launched, or where someone can walk the shore for a great distance, Dickerson said, which are two very different kinds of access.

To be useful in the Sears Island group’s efforts to reach consensus about the largely undeveloped island, more information is needed, he argued.

“The values of conserving at least a substantial part of Sears Island are not based on that [statistic], but are based on ease of access,” Dickerson said.

Sears Island, connected to the mainland by a broad causeway built in the late 1980s, offers access to vehicles and pedestrians.

Sue Inches, deputy director of the State Planning Office who is assisting in the Sears Island planning process, said Tuesday she was not sure where the request for information about publicly accessible shoreline came from, but that it might have been one of many requests compiled by steering committee members and members of an education subcommittee.

Parker’s report noted that Waldo County has 172 miles of shoreline, with at least 22 miles publicly owned. Nearby Hancock County has 1,714 miles of shoreline, with at least 237 miles conserved.