EarthObserver
App© Instructions
Opening the App
Upon opening the app you will see a screen filled with the Basemap. The
map will be at first in shades of gray and turn to color once all the
required content is loaded. The Instructions are obtained by touching
the
Instructions icon that disappears as soon as the
map is manipulated. Exit the
Instructions by touching
the
Back button on its toolbar.
Using the App
The Basemap map is the Global Multi-Resolution Topography synthesis of
sun-illuminated relief of the land and ocean floor created at Columbia
University. You pan the map by dragging a finger across the tablet
surface, and you zoom in by separating two fingers in contact with the
glass. A thin green border around the map indicates that you can
continue to zoom in. A red border warns that you have reached the
maximum detail for a particular region. You zoom out by closing two
fingers in contact with the glass. The map is continuously refreshed by
bringing in new tiles via either a WiFi connection or 3G on the iPhone
or 3G-enabled iPad. The application will not refresh beyond the inital
global view without a working internet connection. When zooming or
panning, the momentary yellow lines are borders of individual tiles that
are being requested from servers. These yellow lines disappear after the
required tiles have been fetched successfully. The content for the
viewport is obtained from the internet and does not require permanent
storage on your device. A limited number of recently-fetched tiles are
cached on a first-in and last-out basis to improve performance and
retain content in the regions recently viewed. The scale bar in the
upper right of the mapview updates according to the zoom level and its
geographic location.
Re-Opening the App
Upon re-opening of the app, the view appears with the Basemap at the
zoom level and location of the last session. This temporary
"bookmarking" allows you to continue where you left off prior
to answering your phone or using another app.
Finding Content
When touched the ">" icon in the lower right corner of
the screen opens a Menu Panel over the mapview with a scrollable list of
available content to overlay on the Basemap. You select a map projection
using the buttons on the top of this panel (Mercator [default], North
Polar or South Polar). The Done button in the lower
right corner of the Menu Panel returns to the map view. The
Camera button in the bottom right center of the Menu
Panel creates a photo of the current map view and stores the photo as a
jpeg file in your Pictures folder. The source of the layer content is
credited in the lower left corner of the map view. The
Gear-Shaped button in the bottom left center of the
Menu Panel opens a Preferences Panel with on/off switches that allow you
to enable or disable the appearance of legends, scale bar, place names
and dim the Basemap in order to highlight regions where the elevations
and depths are available in high-resolution. The Done
button in the lower right corner of the Preferences Panel returns to the
Menu Panel.
Choosing Layers
You select a layer (topic) to overlay on the Basemap by touching its
title. If the "i" icon to the left of the title
is touched instead, this action opens a brower with a description of the
content for that layer along with data sources, credits, citations and
links to other web sites for further information. Touching the
Done button in the web browser returns to the Menu
Panel. When a title with an arrow after it is touched, a child Menu
Panel appears with a scrollable list of further layer choices related to
the parent topic. The Back button returns to the parent
Menu Panel. The Done button returns to the mapview with
the selected layer displayed. Note that the Basemap is always the
default layer unless another choice is made. Following the selection of
a layer and the touching of the Done button, the
selected layer will appear, but in some cases it may be necessary to pan
across the screen or zoom out to the global scale in order to locate its
content.
Changing the Opacity
Upon the selection of any layer except the Basemap, a slider bar appears
in the bottom left portion of the map view in portrait mode or on the
right side in landscape mode (on the iPhone and iPod touch). Touching
and then moving the slider button to the left in portrait mode or down
in landscape mode causes the overlay layer to become more transparent.
Only one layer at a time can be overlaid on the Basemap.
Finding Further Information About a Layer
After choosing a layer and viewing its image in the map window, you will
notice the "i" icon in the lower left corner of
the map window. Touching this icon opens a brower with a description of
the content for that layer along with data sources, credits, citations
and links to other web sites for further information. This action is
identical to touching the same icon in the Menu Panel. However, the
action in the map window allows you to view the information without
going back to the Menu Panel and finding the choice currently being
viewed.
Displaying Values
For many, but not all layers (certain Geologic Maps with complex
textures) you can tap on the displayed overlay layer and the value or
description of the layer at the selected spot is shown and marked with
the apex of a triangle.
Legend Appearance
Because of the limited size of the mapview when using the iPhone and
iPod touch, legends only appear in the landscape mode on these devices.
Scale Bar Accuracy
As a consequence of the distorting nature of the three flat map
projections, the scale bar is an accurate representation of distance
only for the region directy under the scalebar.
Bandwidth Limitation
When using the iPhone with the 3G connection, the app will fetch tiles
at its normal rate upto a threshold of 2.5 megabytes and then throttle
down so as not to fetch more than a total of 5 megabytes of content over
a five minute span. If you are not constantly panning and zooming, you
will probably not notice this limitation. There is no bandwidth
limitation when using the WiFi connection to the internet.
Automatic Cascading of Maps and Charts
The USGS topographic sheets, the NOAA nautical charts and the Geologic
Map of France come from their originating sources at different map
scales. In these cases, we have combined each into a superset of tiles.
Thus as you zoom in for greater detail, the style of the map or chart
may abruptly change due to automatic selection from differently scaled
materials. The layer for the Geologic Maps for the US States first
appears as state outlines, each filled with a different gray value. The
Geologic Map for a particular state is selected by panning across the US
so that the desired state moves to the center of the screen and by
zooming in so that this state occupies more screen area relative to
surrounding states.
Datums and Projections
All content is transformed into and displayed in the WGS 84 coordinate
frame for the Earth. WGS 84 uses the 1996 Earth Gravitational Model
(EGM96) geoid, revised in 2004. The corresponding EPSG Projection codes
are 3857 for the spherical Mercator Projection, 32661 for the North
Polar Stereographic Projection and 3031 for the South Polar
Stereographic Projection.