Latest Contributions by hhet

yes the process of rendering maps in a gis is a process of converting the map to numbers.  absolute location  might also be important to fixing the map to the analysis frame.  street addresses cannot be referenced without absolute location. you have already stated the standard ways to encode  earth locations [lat/long, utm, state plane, etc]. encoding maps requires .a conversion to numeric code. ... View more

dividing a total "count" by an areal extent will give you a relative measure of your variable. the final units are aka density.Density is a relationship. in arcGIS 10.1 , you use Layer Properties to draw quantities using symbol size to show relative value by chooosing the appropriate fields for both Value and Normaliztion. Larger areas may or may not influence the numerical values you want to classify. What you are doing in this calcaulation is deriving  spatially intensive data from spatially extensive data. dividing one sum (as in, summary statistic) by another sum will yield you a spatially independent (of size) unit. Note that areas and perimenters are also considered summary statistics. if you split the areal unit and recalulate (but first you make the basic assumption that the counts are uniformly distributed across the area),  the density value will remain the same as before but the counts and the area will not say the same. Proportions, though calulated differently than density, are also spatially extensive. spatially extensive data should not be used to symbolize a chorolpleth map although this mistake is made over and over again by the uninitiated h ... View more

some questions you might ask yourself before deciding on the choropleth route. 1) is the phenomena evenly distributed throughout the enumeration area?   i f the density of the phenomenon is more not less uniform then  a choropleth map is appropriate 2)does the phenomenon change at enumeration unit boundaries? if so, then choropleth is appropriate. 3) is there a significant variation in  size and shape of the enumeration units? If so, choropleth map may not be advised When you select data to include on a choropleth map you must be sure to adjust the raw totals. do the raw totals involve area? you might consider mapping rates All standardization undertakings have their own computational methods. even though all computational techniques involve ratios, ratios, by themselves are usually not  enough of course, each standardization approach would lead to a different map if you map raw totals , use proportional symbols The answers to these and other questions about designing and constructing  the map   will help determine how accurate your map is using a choropleth technique h ... View more

Re : are tables really feature classes?      in a review of geodatabse fundamentals:                ---as was said earlier, the geographic representation of an object - feature  is stored as one of its                columns (fields) in the row.  the name of the field might be "geometry"                 ----a feature class is managed in a single table                ---in a feature class table each feature class is managed as a table                ---one can create feature classes aka spatial tables               ---one can create feature classes from  xy tables    It appears that the two are not entirely interchangable but dependent on each other. Question is: Is the converse of the original statement true, false or utter nonsense? ... View more

We know that turbulent waters contain more dissolved oxygen (DO).  Higher DO correlates to a greater  ability of a river to purify itself.and is more beneficial for aquatic life. DO affects other water quality indicators such as  clarity, taste and odor.  We might ask where these varied residents obtain their drinking water from. Higher DO gives water a better taste than it would have otherwise, for example. DO is one water quality parameter which may assist your study.  You might need to show whether the water quality (which can change --for better or worse --depending on one's location on a riverway) is in fact, better upstream.  This is not always the case as already stated above. The wealthy can most times avoid floods by locating upstream. The residence times of rivers is  short compared to glacerier and lakes, for examples. To reiterate, you might have to show how the water quality changes as the river water water flows downstream Good Luck ... View more