The Minnesota Clearinghouse Data Delivery Service allows you to choose
geographic themes, choose a spatial area of interest, and extract data for
those themes for just your area of interest. This site is envisioned primarily
as a data distribution tool rather than as a mapping tool. The on-screen
mapping capability, along with the associated data documentation, allows you to
preview the data and decide whether the data is appropriate for your planned
use. Several data delivery map services are planned, each supporting a
different category of data (for example, boundaries, hydrography,
soils and land use.) The Data Delivery Service page is made up of a number of
features:
The Map View Screen enables you to preview the data themes and decide
what you wish to download. Use the Theme Layer List to the right of the map
view screen to specify which layers you want to draw. Use the tool buttons in
the lower left corner of the screen to pan and zoom within the map, and to
query map layers. A default theme is on display when the user first enters the
application.
The Theme Layer List enables you to specify which map themes you wish
to draw in the map view screen. The Theme Layer List includes three boxes, each
of which contains an identical pulldown list of data
layers available for this theme. You may pick a different theme in each box,
and display up to three themes. If you wish to display a theme, highlight the
theme in one of the boxes and check the visible checkbox to the left of the
theme name. If you wish to query on a theme, check the active button to the
left of the theme name.
·
The Visible checkbox indicates which themes the user wishes to see the
next time the map is redrawn. Multiple theme can be
checked to be visible at the same time. ( Some
combinations of theme may be more difficult to distinguish than others when
they are displayed simultaneously.) Important
Note: Some data themes, such as wells, minor watersheds, minor roads,
imagery, etc., are very dense and would not display well as a statewide extent
within the map view screen. These themes are set up to be scale-dependent that
is, as a certain scale, as appropriate for the data set,
these map themes become visible on the screen.
·
The Active button can be used to indicate one of the map themes. This theme, once designated as active, can
be queried for instance, you can then use the identify button to find out
information about a specific feature, or use the query button to select
features based on characteristics of that theme. Only one theme can be active
at a time.
·
The Metadata button provides documentation, or metadata, for the map
theme. Metadata describes the origin, purpose, scale, attributes, and creation
methodology of the data set. It is another tool to help you evaluate whether
this data set is appropriate for your purposes. This metadata is created
according to the Minnesota Geographic Metadata Guidelines (MGMG).
The Refresh button redraws the map view screen with the current set of
visible themes as specified by the user.
A Legend
appears below the theme list referencing all the themes chosen by the user.
This legend area will include a scrollbar if the legend length exceeds the
available screen size.
The Tool Buttons are displayed in the lower left hand corner of the
screen. Tools available to the user include:
Zoom
In - Zoom into the map to show a smaller area. After clicking the
zoom in button, draw a rectangular box on the map viewing screen with your
mouse. The map area will automatically be redrawn to match the areal extent that you indicated. At a smaller areal extent, more layers may become visible on the screen.
Zoom
Out Zoom out of the map viewing screen to show a larger area.
The actual extent of the zoom is determined by the system. You can, however,
indicate with the mouse the point from which you wish to zoom out.
Identify
Use this button to find out more about particular features
within a map theme. This option only works on the Active layer, so first
indicate which theme you wish to make active. Once you have clicked the Identify
button, move the mouse to the map feature you want more information about. The
application will return information about the feature from the files feature
attribute table. This information is displayed in the lower right-hand corner
of the screen.
Pan
Use this button to move around on the map to display
different areas of the map at the scale you have chosen. Place the cursor at a
point within the map view screen, and drag the mouse to pan the screen.
Download
- Use this button to download data. All data sets are in ArcView shapefile format. When
the download button is activated, the application will clip all data themes
checked as visible to the areal map extent displayed
on the screen, then zip all data together and begin a download routine which
will ask you where you want to store the data on your local machine. The data
set downloaded is a zipped file containing shapefiles
of all of the selected layers for the area of interest. Note: The clip option used will include all polygons which are partially
contained within the bounding box. If the polygons were actually clipped to
coincide with the bounding box, then some attribute information associated with
the clipped polygons might be corrupted.
Overview
This option activates an overview map of the state,
highlighting the area selected. This overview map appears in the upper
left-hand corner of the screen.
Full
Extent This option brings you back to the full
extent of the map i.e., the entire state.
Last
Extent This option brings you back to the
previous areal view of the data, before your last
zoom in. This option can be used multiple times.
Query
This option only works on the theme which is chosen as
active. Activate the query tool button to build a query based on attributes of
the data set for example, all lakes with areas greater than 50 acres and draw
only those features to the map when a refresh is done.
When you activate the query tool, an
entry screen appears in the lower right corner of the screen. This entry screen
consists of text boxes and buttons to help you contruct
the query. In the Field textbox,
enter the data field on which the query should be based. A pulldown
list will list all data fields from the layers attribute table. Highlight the
field which will be used to make the query. Then choose an operator from the
Operator Textbox pulldown list. (Operators include =,
>, <, >=, <=, and LIKE). Then input the value for the feature into
the Value textbox. (Character features need to be inside quotation marks). A
Sample List of values is available by activating the Sample Values button. This
retrieves the first 50 records from the database and lists their values in a pulldown list. Because of the size of these databases, this
generally represents just a small subset of the values available. When you have
typed in or selected a value, hit the Add to Query String button. You may
extend the query by hitting the Boolean buttons to the far right of the query
area (And, Or, Not, (, ). Then you can add another query. When you have
completed all query entries, hit the Execute button to begin the query.
When the query has been completed,
several things will happen. The selected features are highlighted in yellow in
the map view screen. The attributes of the selected features are listed in the
right-hand corner of the screen. An option appears to Zoom to Selected Records.
Pushing this button zooms the map view screen in to
encompass just the selected features.