Layers The central concept of this application is the layer, which contains one type of data, like roads or a geological map. You can think of a layer as a sheet of transparent plastic with information printed on it. Each version of the application has a slightly different list of layers. This is because it would not make sense, for instance, to have an earthquake layer for Florida, or a glacial boundary layer for Arizona. The layers are listed in the page for each individual version. You can show and hide layers by selecting the Layers tab at the bottom of the screen. Scroll up and down the list and use the On/Off switch to control individual layers. Keep in mind that the more layers you display, the longer refreshes will take.
You can change the order of the layers by tapping the Move layers button in the upper right corner of the layer list. This allows you to define which layers are on top of which other layers. To move a layer, grab it by using the button on the right that appeared when you tapped the Move layers button. It may be easier if you hold your finger down for a second to really "grab" the layer. Tap the Done button in the upper right corner when the layers are in the desired order.
Each layer has its own transparency, which defines how much it lets the underlying layer(s) through. This is useful when you need to see two or more layers at the same time, but they overlap each other. To change a layer's transparency, as well as some layer-specific display options, select the Layers tab at the bottom of the screen, and tap on the desired layer.
Details You can tap anywhere on the map to get details about the data displayed near that point. This will bring up a list of details ordered by layer. For most layers, you can then tap on a row to get further details. This is indicated by the blue arrowhead at the right of the row.
The details screen looks different for each layer, depending on what information is available. See the full list of layers for more details.
Tools You can select a tool by tapping the Tools tab at the bottom of the screen. You can then select one of the following tools:
Pan/zoom : this is the default mode that allows you to move around the map, zoom in and out, and view details. To zoom in and out, use the standard two-finger swipe-in/swipe-out gestures.
Distance : in this mode, you can measure the distance between any two points on the map. Tap the Done button when you are done.
Area : in this mode, you can measure the area defined by points that you place on the map. Tap the Reset button to start a new area. Tap the Done button when you are done.
Show location : places a "target" icon on the map showing your current location. Note : there is typically a 5-10 second delay initially as the iPhone acquires its position. The target will move along as your position changes. The Center Location tool will put the target at the center of the screen. If the target was not displayed before, you may need to reselect the Center Location tool after a few seconds.
Show grid : adds a grid overlay on top of the map to show longitude/latitude.
Snapshot : takes a screenshot of the current map and places it in the iPhone's Photo Album. If you select the High-resolution option, a high-definition (1920x1280) screenshot of the current map is placed in the iPhone's Photo Album (this may take a while depending on how many layers are shown, and how complex they are). Note that, due to a bug in the iPhone software, the preview may appear blurry in the Photo Album. The picture will look fine when you download it to your computer.
Show distances : puts two concentric circles on the screen showing the scale.
Reset zoom : resets the map to show the entire state(s).
Bookmarks : opens the Bookmarks page where you can save the current state of the app, including which layers are shown, the current location and zoom level, etc... You can also recall one of the bookmarks and reset the app to it.