st_distance(tr_co)## Units: [m]
## [,1] [,2]
## [1,] 0.00 19555.86
## [2,] 19555.86 0.0019555.86/1609 ## [1] 12.15405st_distance(tr_co)## Units: [US_survey_foot]
## 1 2
## 1 0.00 64041.12
## 2 64041.12 0.0064041.12/5280 ## [1] 12.129st_distance(tr_co)## Units: [m]
## 1 2
## 1 0.00 19536.16
## 2 19536.16 0.0019536.16/1609 ## [1] 12.1418Repeat this process, but use the NAD83 layer instead. What is the distance between the two points? Is this distance interpretable?
When using the NAD83 layer the distance I get 12.15405 miles as a result which is different from the Texas South Central layer where I get 12.129. The NAD83 layer uses a geographic coordinate system which provides latitude and longitude. This is not what we usually used in every day life unlike the projected coordinate system which the Texas South Central layer uses that is a metric that is more helpful to us for measurement purposes. Additionally, the decimal degrees used in the geographic coordinate system is non linear and does not measure areas.
Reproject the layer into a new coordinate system, use NAD83 / Texas Centric Albers Equal Area. Re-measure the distance. How does it compare to the one you got using the Texas South Central projection?
You get two different distances. The Texas South Central projection says the two campuses are 12.129 miles apart and the NAD83/Texas Centric Albers Equal Area layer projects the two campuses being 12.1418 miles apart. While the difference can be argued is not too big and the discrepency was less than the layers discussed in the previous questions, we should strive for accuracy when creating maps and using them to measure distances. In this case, the NAD83/Texas Centric Albers Equal Area layer uses the conic projection that is used for countries that are larger horizontally than vertically like the United States so areas are proportional. This is also why scales in maps should always be included s well.
In general, why is it important to have an accurate system of projection? How could your results be sensitive to this?
It is essential to have an accurate system of projection or at the very least a consistent system of projection because you may be mapping locations a lot closer to one another. For example, if you are mapping polling locations for an election, these tend to be multiple voting locations in a fairly small given area. Additionally, when mapping something like this, you are creating a resources for community members that may not be well versed in this topic and so they are fully dependent on the map to find a place to vote. Inthe past, it has made a difference in voter turnout when a GPS location takes you to one side of a building instead of another and voters walk away without voting.