Line-of-Sight and Multipath – GPS’s requirement of a “line-of-sight” means there can be few obstructions between your GPS and the satellites it uses. Practically speaking, this means a GPS will not work inside your home, underground, and may have problems in cities with tall buildings.
Multipath interference occurs when the GPS receives its signal directly from the satellite but also a reflected signal from the same satellite. This interference may cause problems in mountainous regions and, again, in areas with tall buildings. For better reception, some GPS units allow for external antennas mounted outside a car, for example. According to Mark DiMartino, a sales specialist and GPS guru at outdoor equipment retailer R.E.I., newer units have an omni-directional antenna that need not be pointed in any particular direction to achieve line-of-sight reception.
Waypoints – These are locations on the Earth where you want to go. Examples of waypoints are cities, the intersection of two roads, a lake or your own back yard. Once designated, the GPS provides a multitude of information about the waypoint, such as distance, directions to get there from your current location, travel time and much more. Some users will happily designate a few waypoints per trip, never approaching their unit’s limit (ranging from a few hundred to several thousand), while advanced users may store thousands wishing they had room for more.
Routes – Combining waypoints together for a given trip becomes a route. Since most trips are not “as the bird flies” but along paths traversing several places in-between, routes become important. Some sophisticated automobile GPS units intelligently create your waypoints and routes just from knowing your current position and destination. But the majority of units require programming this data manually. Most units will store at least 20 routes in memory at one time. For most, this is plenty, but some will require more.
Track Log/Breadcrumb Trail – Traveling with a GPS, past positions are recorded into a track log. This log remembers where you have been and can help you retrace your path – whether you’re on foot, in a car or boat. This is quite useful when traveling in parts unknown. Since units plot the track log as a breadcrumb trail – a series of dots indicating where you’ve been – if you get lost, you can always follow the trail back. The more track log memory the GPS receiver has, the better.
LCD Display – All GPS units display their information on an LCD screen, similar to that found on handheld computers or PDAs. The better units include high-resolution color displays. These are easier to read but they consume more batteries. Less expensive units come with harder-to-read gray-scale displays. Displays are a large factor in the price of GPS units.
Basemaps and Downloadable Maps – Most GPS units come preloaded with a set of basic maps, or “basemaps.” Without these, the GPS would only indicate your position in terms of latitude and longitude or with a breadcrumb trail. Some GPS devices augment their cartographic abilities with maps you can buy and upload from a computer. Depending on your travels, GPS mapping requirements will differ. It never hurts to have a solid basemap and the ability to add maps in the future.
– Daniel Saltzman