Back when the earliest digital maps for freshwater lakes began to appear on chart plotter screens, I was struck by how different they were.

Some were simple lake outlines - little more than a big, blue area surrounded by a vague approximation of the shoreline. Better versions had more-accurate shoreline detail and showed you at least some depth contours.

The best map cards included hard-to-find details like submerged road and railroad beds, building foundations, pipelines, old power line rights of way and other fish-attracting features that get harder to find as time removes the standing timber from our reservoirs.

Similar map differences exist today.

The built-in base maps that most units come with work pretty well until you zoom in looking for real fishing detail - beyond a certain zoom level the detail just seems to disappear. The plain truth is that if your base map has to cover the whole United States there simply isn't enough memory available to cover each lake in much detail.

Through the years, computer downloads or plug-in memory cards have provided us with increased local map detail. They ranged in coverage from whole regions of the country down to individual lakes.

Memory cards are now the most-popular way to get that extra detail, and advances in computer speed and memory capacity now enable each map or chart card to cover all the popular lakes in at least one or two states with exceptional detail. The quality and quantity of the detail still varies between cards, and the latest version of a card usually holds the best information.

Saltwater coastal charts are made with government survey information that is regularly updated with changes made by major storms and when new hazards to navigation are discovered. Navigable rivers and bodies of freshwater used for commercial shipping and transportation are also covered by official government charts - but the great majority of the lakes we fish are not.

Most maps of man-made reservoirs were originally made from U.S. Geological Survey maps of the lake bottom topography as it looked before it was flooded. They were accurate when the lakes were formed, but decades of erosion, silting and stress from high- and low-water periods have changed their topography and general appearance. Think about how you looked in your grade-school picture in comparison to how you looked in your wedding pictures.

Today's fishermen want maps that accurately depict present-day lake bottoms and shorelines. We want to know where to find natural and man-made fish-attracting structure, and we want to see the lake bottom in finer contour definition than was found in most of the old survey maps.

The answer for several makers of digital maps is to survey lakes with boats equipped to continuously geo-reference GPS positions with sonar soundings and do it precisely enough to form maps with contour lines in as fine as 1-foot increments.

Not all lakes have been surveyed by all map makers, and all digital maps are not created equal; some cover particular lakes or coastal bays in more detail than others, and some maintain better detail at higher zoom levels. You have to shop by looking at your favorite waters on each company's map card, and then buy the one that shows what is under your favorite waters in the best detail. Map samples are often available at a company's Web site, but the best way to check them out is to visit a dealer and see one demonstrated or hit the water with someone who has the chart or map card you are considering.

You might find that a combination of maps serves you best. Years ago, I discovered the built-in map on a Lowrance unit I was testing showed roads and launch ramps better than the super-detailed Navionics map I was fishing with. I found myself going into the unit's menu and switching back and forth between the maps as I planned trips and fished them.

I believe that the more different kinds of electronic cartography a unit can use the better. Chart card manufacturers offer regional maps in several levels of detail, and the top-line products offer special features like 3D views above and below the water, and some even add satellite photos and aerial shots of marinas. Some units are only compatible with maps and charts sold by their manufacturer, while others also let you use third-party maps from international companies like Navionics and Jeppesen/C-MAP.

The maps coming from the unit's manufacturer are usually the least expensive, but those from third-party map makers generally (but not always) have better detail.

Third-party maps from Navionics and Jeppesen/C-MAP (the two international giants in the industry) have historically been available only in manufacturer-specific formats, and unit makers had to design their chart plotters to be compatible with one or the other. You could compare their cartography to software designed to run only on Mac or PC computers.

U.S.-based map maker LakeMaster came at the problem from the opposite direction and designed mapping cards to work with specific chart plotter brands (LakeMaster was acquired by Johnson Outdoors, and its future cartography will only be compatible with Humminbird chart plotters).

The brand-specific limitations may be easing a bit. Coastal and river fishermen using certain Navico units (Lowrance Elite 7, HDS generation 1, HDS gen 2 and gen 2 Touch; Simrad NSS, NSE and NSO; B&G Zeus Touch multifunction navigators) can now use C-Map's MAX-N Wide cartography in addition to all the kinds they are already using that includes Navionics.

A C-MAP MAX-N Gulf of Mexico, Great Lakes and Rivers chart card will cover the Gulf coast from Brownsville, Texas, to Boca Raton, Fla. It also covers the Great Lakes and many of the major rivers between them and the Gulf.

A USA East Coast and the Bahamas chart covers the Atlantic coast from Passamaquoddy Bay, Maine, to Key West, Fla., with extended coverage into the Gulf over to Perdido Bay, Fla. It also covers several eastern U.S. rivers, Bermuda and the Bahamas.

Making sure that your chart plotter is equipped with its manufacturer's latest software update is a common-sense prerequisite to running any newly introduced or updated cartography. I'd like to see the ability to use both Navionics and C-MAP cards become a trend and develop to the point that units could run all of either company's inland and coastal cartography. It also wouldn't break my heart to see Johnson Outdoors rethink its decision and open up LakeMaster's excellent inland lake mapping for use in more than just Humminbird units.

The more compatibility we have in the world of electronic mapping the better chance we have to zero-in on the ideal chart plotting solution for our personal inland and coastal fishing needs.