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About the Map Viewer - Frequently Asked Questions

What is the Calflora Map Viewer?
The Calflora Map Viewer is a web application for visualizing where wild plants have been observed, by showing colored points against a relief map of California. By clicking on a point, you can see the corresponding observation record.

The viewer will zoom to fifteen different levels. To make the location of observation points more comprehensible, the viewer offers various optional features including roads (two levels) and a grid. The viewer can show labels on the map; for instance, the names of towns, mountains, streams, etc.

The viewer can also show shaded polygonal areas, such as those indicating watersheds (from Calwater 2.2, at five levels), or GAP plant community regions.

Sometimes a set of observations is linked to a polygonal area (such as when a botanist made a list of all plants within the boundaries of a particular state park). When this is the case, the viewer can show these observations either as a shaded polygon or as points.

How do I start the viewer?
To start the viewer, enter a query to the Calflora Observation Library, For instance, look for Artemisia californica in Santa Barbara County. If there are any georeferenced points that match your criteria, the results page will show a small map of the county and a link to the map viewer that looks like this:

Click the button, and the viewer will come up showing all of Santa Barbara County, and points indicating where the plant has been observed.

How do I use the viewer?
Use the control on the left side of the screen to zoom in or out. Use the small beige map in the upper right to re-center the map. (Note that you can use this control to move anywhere in the state).

If it is too difficult to see the points or the names, use the Relief Intensity control to soften the relief layer. You can also turn the relief map completely off (best for printing).

The color of the points indicates documentation type -- for instance, blue points indicate specimen data. Mouse over a point to see the location description and species observed. Click on a point to see full details of the observation(s).

Where does the map data come from?
The Calflora Map Viewer has two basic parts: a map server, and a user interface.

The server generates images from 1. raster data (image files showing relief features), and 2. vector data (points, lines, and polygons).

The server uses a library of raster data for the relief layer, consisting of JPEG image files generated by GlobalMapper from USGS NED and DEM files.

The server uses a library of vector data to generate a foreground image (superimposed over the relief layer by a web browser). The foreground image contains observation points and any user-selected features (roads, streams, various polygons, names, etc.).

Source data for the vector library comes from many places. Roads, lakes, and the coastline are from US Census Bureau Tiger/Line files. Streams are from the USGS National Hydrology Dataset. The names and positions of towns, mountains, etc. are from the USGS Geographic Names Information System.

Polygons for East Bay regions were prepared by Heath Bartosh for the East Bay CNPS Rare and Unusual Plants Program (EBRUP) and generously contributed.

Polygons for many parks and reserves are from the California Spatial Information Library, Public, Conservation and Trust Lands (PCTL) dataset. Polygons for Bay Area Open Space areas are from Greeninfo Network. Other polygons were contributed by the Sonoma County Agricultural Preservation and Open Space District (Tom Robinson), Monterey Peninsula Regional Park District (John Schweisinger, Turf Image), and the Land Trust of Napa County (John Hoffnagle).

Point locations come from the Calflora observation database, in decimal latitude/longitude format, NAD83 datum.

Why doesn't it show the other points?
On the result page for an observation query, you may see a message like the following:

    The map shows 3 out of 5 available georeferenced point(s).
In a case like this, the unshown points are very close to the shown points. They are so close that even at the maximum zoom level, you would not see them as distinct.

I asked to see observations of a particular species in county X, and the map shows points in county Y.
This is data problem. The point georeferenced within county Y is labeled as being in county X, so it appears when you ask to see things in county X. Either the georeference information is incorrect or the county label is incorrect. You can contact the data contributor and point out the discrepancy.

Also, as you look at the points, bear in mind that each point has a location precision. For some points it may be a few feet; for others as much as a mile. For such imprecise points, the plant was observed somewhere near where it it shown, but probably not exactly where it is shown.

Data contributors: if you think Calflora is incorrectly displaying some of your data, please contact us and we will try to fix the problem.

Can I bookmark a map viewer page, or send the URL to a friend so that they can see exactly the same map?
When the map viewer is first invoked from the Calflora plant observation query results page, it uses the post method to accomodate potentially voluminous point data. Notice that in the browser URL field, the URL has no no parameters such as zoom level or center point. If you were to bookmark the page, the position and size of the map you are seeing are not included in the bookmark, so when you return to the bookmark, you end up in the viewer's default location (western Nevada).

If you want to bookmark a particular map, there is a link labeled

    Link to this page
on the bottom right. If you click on the link, the browser will show the same map, but the URL will be bookmarkable. If you want to email the page to somebody, you can right click over the link and select Copy Link Location or Copy Shortcut, and then paste the URL into an email.

What are GAP Plant Communities ?
The California Gap Analysis Project was completed in 1998 and published by the Biogeography Lab, University of California, Santa Barbara. Data from the project includes over 27,000 polygons covering the state, where each polygon is identified as to plant community (according to the Holland system) and wildlife habitat type (according to the California Wildlife Habitat Relationships system). The purpose of the project was to find plant communities or species (plant and animal) potentially at risk because they occur primarily on private land. (As an example of how the data has been used, see Biodiversity in the Southwestern California Region, David M. Stoms and Frank Davis.)

The GAP polygons are included in the Calflora Map Viewer as an optional background to provide a sense of local context for the plant observation points. For instance, if you see that a plant observation occurs in an area identified as Alluvial Redwood Forest by the GAP data, that may give you a rough idea of the immediate environment in which the plant was growing.

There are many things to bear in mind when looking at the GAP data. As prepared by the GAP project, each polygon has a primary plant community. Some also have secondary and tertiary plant communities. The map viewer shows only the primary community. For any polygon, the primary community is understood to be the most important community in the whole area of the polygon. There may be areas of other plant communities within a polygon, which are not represented in the data or on the map. For example, the entire County of San Francisco shows on the map as Urban or Built-up Land, but in fact there are relatively small areas of costal scrub and various dune communities present there. For another example, on the coast of Mendocino County, what shows on the map as large areas of Bishop Pine Forest actually has smaller ares of coastal scrub and coastal prairie within it. In general, plant communties occurring in small areas (e.g. riparian corridors) are under-represented in the data. If you know a natural area well, you will probably find its representation in the GAP polygons to be overly simple.

In spite of any limitations, the GAP data can supply a useful level of background information, and there is no other dataset that matches it for completeness or detail. Visual presentation of the data dramatizes

  • the amount of land that is primarily urban or agricultural, and
  • the complexity of the California landscape, and how much work it would take to map it more fully.

    The basic technique of the GAP project (analysis of aerial photos plus site visits) has since been improved upon; see particularly the Napa Vegetation Mapping Project (James Thorne et. al.).

    Finally, is the juxtaposition of Calflora plant observation data with GAP plant community polygons predictive? For example, if you see a point occurrance of some species coinciding with a polygon representing a redwood forest, does it mean that that species grows in redwood forests? The simple answer is no, because the data is not detailed enough. But, used in conjunction with other sources of information (e.g. the location description of the observation, or the coincidence of many points of the same species with a single plant community), this data may help to strengthen or weaken such a prediction.

      Map View User Interface. When you first turn on GAP Plant Communities, the viewer selects all GAP polygons that overlap the currently selected map area. The viewer groups these polygons by community, sums the cumulative area of each community, and sorts the communities by area. The list of communities represented in the current map appears at the bottom of the page. By default, the viewer selects the three largest communities, and shows the polygons associated with these communities shaded in various colors on the map. You may select any communities you would like to see shaded, and press Redisplay.

      By default, similar communities are displayed in the same color (there are 200 communities and 30 colors). For instance, all coastal scrub communities are displayed in the same color. If more than one coastal scrub community is represented in the current map area, and you would like to see each shaded with a different color, then select the Use a different color for each community option at the bottom of the page.

      The Holland system of plant communities was in use by the Califormia Natural Diversity Data Base in the 90's, but was never published and has since fallen out of use. Thus, as of this writing, there is no place on the web where these communities are fully described. The closest is a translation table between the Holland communities and series from A Manual of California Vegetation, Sawyer and Keeler-Wolf 1995. (See also General Information Regarding Holland Communities.)

    What kind of information can the Map Viewer show?
    Observations of Blue oak, Quercus douglasii, in Shasta and Tehama Counties with GAP polygons showing Blue Oak Woodland
    Observations from UC Riverside Herbarium in western Riverside County above 2000 meters (all species)
    GAP polygons showing Redwood forests in the greater Bay Area
    Observations of yellow star thistle, Centaurea solstitialis, in Tulare County with GAP polygons showing agricultural land
    Observations of Arctostaphylos species around the Bay Area, including regions from the East Bay CNPS Rare and Unusual Plants database, quads from the CNPS Inventory Database, and points from other sources.
    Observations of Arctostaphylos species from Santa Barbara and San Luis Obispo Counties, including quads from the CNPS Inventory Database and points from other sources.
    Observations from the Marin CNPS chapter.
    Observations from the Monterey CNPS chapter, with watersheds at the Calwater 'Hydrologic Area' level.


    Contact us if you have further questions, or suggestions for features you'd like to see or to contribute.

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