Topo Maps :: User Guide

You can move around and zoom in and out on this map using the usual touch gestures. If you zoom out, arrow buttons will appear to navigate to the other satellite maps:

To the North is this map of Canada and Alaska:

To the West is a map of Hawaii, and to the South is a map of Puerto Rico and the U.S. Virgin Islands.

If you zoom in on any of these satellite maps, a yellow grid showing the individual topo maps becomes visible:

Orange markers show the positions of national parks, forests, wildlife refuges and similar areas. Smaller red markers show state parks, etc.

Installing Maps

You can select one of the maps by touching it for about half a second without moving your finger. You'll then be asked whether you want to install the map:

You can choose either a "Quick Install" or a "Full Install". The quick install downloads a lower-resolution version of the map; this can be useful to check whether you have the right map, or to get an overview of an area. For navigation you'll normally want to download the full version of the map.

The map will then be downloaded; how long this takes depends on the speed of your network connection. WiFi may be faster than a cellular connection, but then again it might not. This screen is shown while this happens:

After downloading, for some maps you must then wait for a couple of minutes while the map is installed; the majority arrive in a "pre-tiled" format that doesn't need this installation step.

Apart from installing maps the app does not need a network connection. So once you have installed the maps that you need you don't need to worry about having cellular or WiFi coverage.

If you quit the app by pressing the home button while a map is being downloaded or installed, the incomplete map will be abandoned. If you put the device to sleep by pressing the power button the download may continue; however, this is not normally successful. We therefore recommend that you don't put the device to sleep during a download.

Back on the satellite map, sheets that have been installed are shown in green. Low-resolution "Quick Install" maps are shown in a darker shade than high-resolution "Full Install" maps:

In a few areas, maps overlap. This happens mostly in Alaska, where 1:24,000 maps often overlap with 1:63,360 maps, and on the Canada-Alaska border. In these areas, to select the map that you want, zoom in and carefully touch at the center of the correct map's yellow box.

Installing Multiple Maps

You can install a block of maps at once as follows:

Adjust the satellite view so that you can see all of the maps that you want to install.
Touch a map at the corner of the block that you want to install until it is selected, as if you were going to install just that one map, but do not lift your finger.
Slide your finger to select all of the maps that you want. A blue rectangle is shown; this should overlap but need not entirely cover all of the maps that you need.

Lift your finger.

You'll now be asked if you want to do a Quick or Full install - however, there are limits to the number of maps that can be installed at once. "Full Install" is limited to ten maps at a time, and "Quick Install" is limited to 100 maps at a time. There is no limit to the total number of maps that can be installed in the app (apart from the capacity of your device) - this limit is purely on the number that can be installed in each use of the install function.

Searching

You can search for maps or parks by name using the magnifier icon at the bottom left of the screen. When you touch it the search screen is shown:

Type in the name of a map or of a national or state park, forest, wildlife area, monument etc. As you type the list of search results is continuously updated. The results are grouped into maps, national landmarks and state landmarks. Maps that are already installed are shown in blue. When you find the map or landmark that you want, touch its name.

Viewing Maps

Having found and installed the map that you need, to view it simply touch the green map square for about half a second. The app will now "flip over" to show the map:

Initially the map is zoomed out so that it's all visible. As with the satellite map you can move around and zoom in and out using the standard gestures:

At the maximum zoom you're seeing one scanned pixel for one screen pixel; since the maps are scanned at a higher resolution than the iPhone's screen this is actually larger than the paper maps:

If you used the "Quick Install" mode, as you zoom in at some point the map will be replaced with a message:

Upgrading the map to high resolution is described later.

At the bottom right of the screen a "page curl" button allows you to flip back and forth between the current topo map and the satellite map. (Note that when you install a new map, it does not become the current map accessible via this button until you have selected it by touching the map's green outline.)

If you scroll to the edge of the map, you can see all of the original border material. This includes information about survey dates, map projections and so on:

Map Mosaics

If your area of interest spans the join between two or more maps, you can mosaic them together. First, install all of the maps that you need. Now view one of the maps, and scroll to the edge. An arrow button will be shown:

Touch the arrow button, and the adjacent map will be added:

Mosaics can also be useful for getting a broader view of an area, such as with this triple mosaic:

To revert to showing a single map, flip back to the satellite view and select the one map that you want to view; it will be shown un-mosaiced.

The app doesn't limit the number of maps that you can mosaic together, but you will find that it gets slow if you try to add many.

Note that maps' border material may overlay or show through at the join.

The mosaicing feature relies on the adjacent maps using the same map projection and having been scanned at the same pixel scale. Map projection zones typically change every 6 degrees of longitude, and pixel scales often change at state boundaries and where USGS production methods changed. If the resulting mis-alignment is small the app will mosaic the maps and show a warning; if the mis-alignment is large it will refuse to add the map.

GPS

At the bottom left of the screen, a button with a target symbol shows your current position as reported by the GPS (or Skyhook location on the iPod touch):

When this target is shown on a topographic map, but not on the satellite map, the size of the inner circle indicates the accuracy of the location as reported by the hardware. If the fix is inaccurate, touch the button again; the app will get another fix from the hardware which may be more accurate.

Note that the iPhone's "Airplane mode" disables the GPS as well as the cellular and WiFi radios.

Go To Other Apps

The second button at the bottom left of the screen, with an icon that means "exit", displays a list of other apps and websites that you can use to view the currently displayed area:

The first three buttons go to the Google Maps app in its three modes, "maps", "satellite" and "hybrid". The "OpenStreetMap" button goes to the OpenStreetMap website.

The other two buttons are only displayed if these apps are installed. The "Panoramascope" button runs the Panoramascope app; this is another app by the same author that will compute the view as seen from anywhere on earth. Touching this button will compute the view from the point at the center of the screen; you'll see a view like this (Mt St Helens as seen from Mt Adams):

The "Offmaps" button goes to that app, which is an offline OpenStreetMap viewer, if it is installed . If you know of any other apps that can be invoked in this way (they need a "URL handler"), please get in touch.

Map Settings

The third button, with an icon showing a map and a gear, displays the map settings window:

The top of this window shows the name of the map. Below this are various controls related to the map, described below.

Note that some of the functions are only available when a single map is shown, not when a mosaic is shown.

Up/Downgrade Resolution

Below the map name, the map size (in kilobytes or megabytes) is shown and to the right a button to upgrade to high resolution or downgrade to low resolution, as appropriate.

Upgrading shows a screen very similar to the map installation screen, and a progress bar moves as the additional map data is downloaded. Note that the high-resolution map data is a superset of the low-resolution data, and only the additional data will be downloaded.

In a few cases it may not be possible to upgrade a map. This is most likely because the map has changed on the server, or the map was not pre-tiled. In this case, you should delete the map and re-install it using the "Full Install" option.

You can also downgrade a high-resolution map to low-resolution to save space.

Hill Shading

When you download a map, the app also installs altitude data which is used to add the hill shading effect. You can adjust the hill shading using the two controls in the map settings window:

The slider allows you to adjust the strength of the hill shading. If you slide it to the left, hill shading is disabled. Positions in the middle are appropriate for mountainous terrain. In flatter areas you can move the slider to the right to exaggerate the shading.
To the right, you can rotate the sun and shade around the hill to set the direction of the simulated sunlight. Apparently most people see the 3D effect most effectively if the light comes from the top left (NW), even though this is not a direction from which sunlight ever comes in the Northern hemisphere. If you move the sun to the South you'll see more realistic shading, which could be useful to determine which routes will be most sunny.

This map uses the default shading settings:

Here the strength has been increased:

Here the sunlight direction has been moved to the South:

For comparison, here's the same map with hill shading disabled:

The hill shading is updated after you close the map settings window by touching the close button at the bottom right. It typically takes a couple of seconds for the new shading to be computed for a single map, or longer for a mosaic.

The height data used to compute the hill shading has a horizontal resolution of only about 300 feet, so the results are not very precise. Hill shading is most useful when you're viewing a map zoomed out so that the contour lines are not easily visible. The alignment of the shading data with the base map also seems to be poor in some areas, and there are occasional artifacts such as false grooves and ridges. Better data is available and we may upgrade it at some point.

Erasing Maps

At the bottom left of the map settings window is a button to erase the map. You shouldn't need to do this unless you're running out of space on your device.

Help

The final button at the bottom left of the screen, with a question mark symbol, shows a help screen.

Measure Mode

At the top right of the screen, a button with an arrow symbol enables measure mode. In this mode, fine crosshairs are shown and the co-ordinates at this point are displayed at the top of the screen:

Note that the co-ordinates are for the fine crosshairs, not necessarily for your current position.

You can change the format of the co-ordinates by touching the co-ordinate display for about half a second. It will cycle through the following five formats:

Decimal degrees.
Degrees and decimal minutes.
Degrees, minutes and seconds.
UTM
MGRS / USNG

The datum being used is shown to the left of the co-ordinates; to change between WGS84 and NAD27, touch this display. In Hawaii, Puerto Rico and the Virgin Islands, NAD27 mode shows the appropriate pre-WGS84 datum.

It is recommended that you check the accuracy at the corners of the maps. For WGS84, the co-ordinates will match not at the corner of the map but rather at the cross nearby:

WGS84 should give accurate results everywhere. NAD27 is computed using an approximation that should be within a couple of pixels throughout the contiguous U.S. Accuracy of NAD27 mode may be worse elsewhere.

Co-ordinate accuracy (and also GPS accuracy) may be worse when maps are mosaiced than when a single map is shown. Checking the co-ordinate display at the corners and joins of the maps is recommended.

To the right of the co-ordinates, an approximation of the height at the crosshairs is shown. This is based on the same data that's used to compute the hill shading and it has relatively poor resolution. You should get reasonably accurate values in flatter terrain (for example, large lakes) but summits will rarely be accurate.

Measure mode also displays a distance scale at the left of the screen. You can change the format between miles, feet and km by touching it for about half a second.

Distance and Bearing Mode

Below the altitude display is a button that enables distance-and-bearing mode. To measure distances and bearings, place the crosshairs over one of the points and press the distance-bearing button. A series of concentric distance rings will be shown. As you move the map, the distance and bearing from the selected point to the current position of the crosshairs will be shown at the top left of the screen, below the co-ordinates display:

The units used for the rings and the distance display are the same as those used for the scale and you can change them by touching the distance display or the scale.

The bearing is shown in degrees and you can change between degrees relative to true N and degrees relative to magnetic N by touching the bearing display. The magnetic deviation is predicted using the International Geomagnetic Reference Field; it should be accurate to better than half a degree.

Having selected a point for the distance-bearing mode you can change to a different map and the measurements will continue to be shown:

For very large distances you will start to see discrepancies between the distance shown on the distance display and the rings - 60 miles in the case of California to Hawaii shown above. This is because the distance display shows the great circle distance (which takes into account the fact that the earth is a sphere) while the rings are simple circles. The results should match to within better than 0.1% for distances within a hundred miles or so.

To clear distance-bearing mode, touch its button again.

Measure mode is also available on the satellite map, though only the co-ordinates are shown. This can be useful if you know only latitude and longitude and need to find the appropriate map.

Safe Mode

Normally when the app starts it tries to restore your previous view, including any mosaiced maps. In the unlikely event that the app fails to start properly, "safe mode" can be used to make it start up in a default state. Note that this is not a "factory reset", i.e. it does not erase all of your maps or anything like that. To enable safe mode, from the home screen touch Settings and select Topo Maps:

Move the slider to On, return to the home screen, and start Topo Maps. Startup may be significantly slower in safe mode because it also re-indexes your maps, rather than relying on a previously cached map index.