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LandView® 6 Census 2000 Population Estimator
The major difference in LandView 6 as compared to LandView 5 is the quantum leap in the kind and quality of the data available from the 2000 Decennial Census. Census 2000 data in both LandView 5 and LandView 6 is modeled upon the data tables presented in the Census 2000 Demographic Profiles.
The DP-1 tables, available in LandView 5, contained selected data items plus calculated statistics derived from the 1,040 statistical tables contained in Census 2000 Summary File 1 file (SF 1)-the datasets then available for publication. To Table DP-1, LandView 6 has added Tables DP-2 through DP-4; these are based on selected data items plus calculated statistics derived from the 813 statistical tables contained in Census 2000 Summary File 3 file (SF 3).
In LandView 6, the DP-1 through DP-4 tables are available at all levels of Census geography down to the Census Block Group level. A National Summary button, available at each dataset, allows comparison of local datasets to a National Profile representing composite data for the 50 United States and the District of Columbia.
With this expansion of LandView data comes a revision of the Population Estimator. In LandView 5, a search for population at a radius about a point would search out data at the Census Block level, the smallest unit of Census statistics and its most accurate. This, the Estimator still does. Accuracy comes, however, at a price-data agglomeration. At the Block level, only a limited set of data is available, that displayed in the Estimator dialogue box, shown below 1.
To share the rich demographics available in LandView 6, LandView has turned to the Census Block Group 2. The demographic profile in the Estimator relies on the capture of the centroids of Census Block Groups within the radius of a circle. For any individual Census Block Group, say, 55% of its area lies inside the capture circle, and its data would be included. Another Group might have 49% of its area inside of the circle and it would be excluded. On sum, the capture and loss of individual Block Groups should average out, but not to the degree of precision attached to population search by Census Blocks. It is this dichotomy of data that needs to be borne in mind when interpreting Population Estimator results.
Using the Population Estimator
The Population Estimator can be opened from the Estimate Population within a Radius3 button on the LandView 6 Home page. Normally, the population search is tracking the location of the Focus Point in MARPLOT, and the MARPLOT application should be running before using the Population Estimator. (Other Help files and the LandView Tutorial discuss the interactions of the LandView and MARPLOT applications.) In MARPLOT, once the Focus Point has been set to the desired search point, the Population Estimator is available from the MARPLOT MenuBar,
at Sharing/LandView/LandView Census 2000 Population Estimator. Either pathway opens the Estimator shown below:
In this example, the MARPLOT Focus Point has been set to a location in eastern Virginia. Entered in the Radius (miles) field is a search radius of three miles. The button at Calculate Population using Block points has already been invoked , and we see, that within the capture radius, there is a population of 32,118 persons. The limited dataset available at the Census Block level is shown in the dialogue.
To explore a demographic profile at the same map location, use the Summarize Demographic Profiles using Block Group points button. After calculations, the DP-1 format data screen, shown below, is seen.
When using the Summarize Demographic Profiles Using Block Group points function on either the East or
West DVD, users need to pay attention to whether their radius extends beyond the state boundaries of the
states contained on the DVD. A simple way to determine this is to use the Show this radius on map function.
If a portion of the circle defined by the radius is located in a state not contained on the DVD, the results
will exclude the demographic and housing characteristics for that portion of the circle. In such situations,
we recommend that the user change the threshold for the block group method (which is shown on the Population Estimator Help Screen) to a value smaller than the radius. Doing this will produce a complete demographic profile since it will then be calculated from a national file of tract internal points contained on both the East and West DVDs.
Using the radio buttons in the upper-right corner, we can move from the DP-1 table through tables DP-2 to DP-4. We can print each of these tables. We can compare them to the National Profile or to a profile of the containing City, County or State. More detailed instructions on using the Estimator are available at the Instructions for using this estimator button.
An additional feature of the Estimator is the Show this radius on map button. Using the button, we return to MARPLOT with the search radius displayed as below. However, unless we place it into a context, we learn little. The MARPLOT map screen has been reset to show the network of roads in and around the capture circle.
A final feature in the Population Estimator that bears mentioning is the fact that a population search can be conducted at very large radii. As a radius becomes larger, though, the number of Block points to be searched multiple as the square. At some point the data search can become time consuming. To minimize search time, at a pre-set radius, the search moves from examining Census Block points to examining Census Tract points. The default radius for this is 25 miles 4. Within the Instructions for using this estimator button discussed above, lies an addressable field that allows this default search radius to be changed to meet a user's needs.
Searches for Population at a radius around a point are programmed
utilities within LandView. Searches for population residing within a
defined map area, say a National Park, require some additional effort
on the part of the user. Methods for such searches are explored in an
article in Unique Solutions.
1 There are 8.2 million census tabulation blocks for the geographic areas shown in LandView. 2.7 million blocks are excluded because they contain zero population and zero housing units.
2 There are 211,267 block groups for the 50 states, District of Columbia and Puerto Rico. On the average, each block group contains about 39 blocks.
3 The LandView program's algorithm for determining which block internal points fall within the radius takes the curvature of the earth into account. The MARPLOT mapping engine in mapping the radius does not. Consequently for larger radii, users might note differences in the block point counts between MARPLOT and the Population Estimator.
4 An alternate population search that is frequently of interest is Finding the Population Within an Irregular Polygon. An example of such a search is given in Lesson 5 of the LandView 6 Tutorial.