Homework3/Lab 2

Author

Lydia Okabe

library(tidycensus)
library(sf)

Linking to GEOS 3.9.1, GDAL 3.4.3, PROJ 7.2.1; sf_use_s2() is TRUE

library(dplyr)


Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Read in Bexar county tracts

(Seem familiar? We did this chunk below before in Lab 1/Homework 2.)

sa_acs<-get_acs(geography = "tract",
                state="TX",
                county = c("Bexar"),
                year = 2019,
                variables=c( "DP05_0001E", 
                            "DP03_0119PE") ,
                geometry = T, output = "wide")

Getting data from the 2015-2019 5-year ACS

Downloading feature geometry from the Census website.  To cache shapefiles for use in future sessions, set `options(tigris_use_cache = TRUE)`.

Using the ACS Data Profile

#create a county FIPS code - 5 digit
sa_acs$county<-substr(sa_acs$GEOID, 1, 5)
#rename variables and filter missing cases
sa_acs2<-sa_acs%>%
  mutate(totpop= DP05_0001E, ppov=DP03_0119PE) %>% ##mutate changing file names/renaming it
#  st_transform(crs = 102740)%>%
  na.omit()
##geometry pulls shape file information

Repeat this process, but use the NAD83 layer instead. What is the distance between the two points? Is this distance interpretable?

NAD83 layer (with no transformation)

Answer: Using no transformation, the two tracts UTSA Main and Downtown Campuses are 19.555 meters away from each other. When this is converted to miles, the distance between the two campus is 12.15 miles. The distance is interpretable

##Measuring distance for NAD83
st_crs(sa_acs2) ##finds the coordinate reference system

Coordinate Reference System:
  User input: NAD83 
  wkt:
GEOGCRS["NAD83",
    DATUM["North American Datum 1983",
        ELLIPSOID["GRS 1980",6378137,298.257222101,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["latitude",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["longitude",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4269]]

twtr83<-sa_acs2%>%
  filter(GEOID %in% c(48029181820, 48029110600))
# get centroid coordinates for two tracts (these two tracts are where UTSA Main and Downtown Campuses are)
tr_co83<-st_centroid(twtr83)

Warning in st_centroid.sf(twtr83): st_centroid assumes attributes are constant
over geometries of x

head(tr_co83)

Simple feature collection with 2 features and 9 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: -98.61502 ymin: 29.43017 xmax: -98.50751 ymax: 29.57909
Geodetic CRS:  NAD83
        GEOID                                      NAME DP05_0001E DP05_0001M
1 48029181820 Census Tract 1818.20, Bexar County, Texas       8305        833
2 48029110600    Census Tract 1106, Bexar County, Texas       5293        423
  DP03_0119PE DP03_0119PM                   geometry county totpop ppov
1        15.2         9.1 POINT (-98.61502 29.57909)  48029   8305 15.2
2        37.8        15.2 POINT (-98.50751 29.43017)  48029   5293 37.8

##get distance
st_distance(tr_co83)

Units: [m]
         [,1]     [,2]
[1,]     0.00 19555.86
[2,] 19555.86     0.00

19555.86/1609.3 ##convert to miles

[1] 12.15178

Create Basic Map

library(tmap)
library(tmaptools)
tm_shape(sa_acs2)+
  tm_polygons("ppov", title="% in Poverty",
              palette="Blues",
              style="quantile",
              n=5 )+
  tm_format("World",
            main.title="San Antonio Poverty Estimates (2019) - Quintile Breaks",
            main.title.position=c('center','top'),
            main.title.size=1.5,
            title="Author: Lydia Okabe. \nSource: ACS 2019", ##gives you second title/small title with name and source
            legend.title.size=1.7,
            legend.outside=T,
            legend.text.size=1.2)+
  tm_scale_bar(position = c("left","bottom"))+
  tm_compass()

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

Re-Project Map into “South Central Texas” Projection

new_sa<-st_transform(sa_acs2, crs = 2278)
#Extract two tracts
twtr<-new_sa%>%
  filter(GEOID %in% c(48029181820, 48029110600))
# get centroid coordinates for two tracts (these two tracts are where UTSA Main and Downtown Campuses are)
tr_co<-st_centroid(twtr)

Warning in st_centroid.sf(twtr): st_centroid assumes attributes are constant
over geometries of x

##head
head(tr_co)

Simple feature collection with 2 features and 9 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 2090862 ymin: 13704280 xmax: 2125261 ymax: 13758300
Projected CRS: NAD83 / Texas South Central (ftUS)
        GEOID                                      NAME DP05_0001E DP05_0001M
1 48029181820 Census Tract 1818.20, Bexar County, Texas       8305        833
2 48029110600    Census Tract 1106, Bexar County, Texas       5293        423
  DP03_0119PE DP03_0119PM                 geometry county totpop ppov
1        15.2         9.1 POINT (2090862 13758297)  48029   8305 15.2
2        37.8        15.2 POINT (2125261 13704278)  48029   5293 37.8

st_distance(tr_co)

Units: [US_survey_foot]
         1        2
1     0.00 64041.12
2 64041.12     0.00

64041.12/5280 #To get feet into miles

[1] 12.129

Texas Centric Albers Equal 3083 Area

With transformation

new_tc<-st_transform(sa_acs2, crs = 3083)
#Extract two tracts
twtc<-new_tc%>%
  filter(GEOID %in% c(48029181820, 48029110600))
# get centroid coordinates for two tracts (these two tracts are where UTSA Main and Downtown Campuses are)
tr_co1<-st_centroid(twtc)

Warning in st_centroid.sf(twtc): st_centroid assumes attributes are constant
over geometries of x

head(tr_co1)

Simple feature collection with 2 features and 9 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 1633963 ymin: 7257682 xmax: 1644584 ymax: 7274079
Projected CRS: NAD83 / Texas Centric Albers Equal Area
        GEOID                                      NAME DP05_0001E DP05_0001M
1 48029181820 Census Tract 1818.20, Bexar County, Texas       8305        833
2 48029110600    Census Tract 1106, Bexar County, Texas       5293        423
  DP03_0119PE DP03_0119PM                geometry county totpop ppov
1        15.2         9.1 POINT (1633963 7274079)  48029   8305 15.2
2        37.8        15.2 POINT (1644584 7257682)  48029   5293 37.8

Measure to meters to miles

When measuring the distance the UTSA Main campus and the downtown campus from NAD83 / Texas Centric Albers Equal Area, the data is transformed, the results show a distance of 19536.16 meters. However, in order to convert this into miles, we divide 19536.16/1609.34 and get a 12.13924 distance.

st_distance(tr_co1)

Units: [m]
         1        2
1     0.00 19536.16
2 19536.16     0.00

19536.16/1609.34

[1] 12.13924