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<h1 class="title toc-ignore">Working with Spatial Data</h1>
</div>
<p><a href="04_Spatial.R"><i class="fa fa-file-code-o fa-3x" aria-hidden="true"></i> The R Script associated with this page is available here</a>. Download this file and open it (or copy-paste into a new script) with RStudio so you can follow along.</p>
<div id="setup" class="section level1">
<h1>Setup</h1>
<div id="load-packages" class="section level2">
<h2>Load packages</h2>
<pre class="r"><code>library(sp)
library(rgdal)
library(ggplot2)
library(dplyr)
library(tidyr)
library(maptools)</code></pre>
</div>
</div>
<div id="point-data" class="section level1">
<h1>Point data</h1>
<div id="generate-some-random-data" class="section level2">
<h2>Generate some random data</h2>
<pre class="r"><code>coords = data.frame(
x=rnorm(100),
y=rnorm(100)
)
str(coords)</code></pre>
<pre><code>## 'data.frame': 100 obs. of 2 variables:
## $ x: num -0.7755 1.5926 1.038 -0.0797 -1.6608 ...
## $ y: num -0.0159 0.7206 0.08 0.7659 0.5246 ...</code></pre>
<pre class="r"><code>plot(coords)</code></pre>
<p><img src="04_Spatial_files/figure-html/unnamed-chunk-4-1.png" /><!-- --></p>
</div>
<div id="convert-to-spatialpoints" class="section level2">
<h2>Convert to <code>SpatialPoints</code></h2>
<pre class="r"><code>sp = SpatialPoints(coords)
str(sp)</code></pre>
<pre><code>## Formal class 'SpatialPoints' [package "sp"] with 3 slots
## ..@ coords : num [1:100, 1:2] -0.7755 1.5926 1.038 -0.0797 -1.6608 ...
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : NULL
## .. .. ..$ : chr [1:2] "x" "y"
## ..@ bbox : num [1:2, 1:2] -2.82 -3.2 2.13 2.9
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : chr [1:2] "x" "y"
## .. .. ..$ : chr [1:2] "min" "max"
## ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
## .. .. ..@ projargs: chr NA</code></pre>
</div>
<div id="create-a-spatialpointsdataframe" class="section level2">
<h2>Create a <code>SpatialPointsDataFrame</code></h2>
<p>First generate a dataframe (analagous to the <em>attribute table</em> in a shapefile)</p>
<pre class="r"><code>data=data.frame(ID=1:100,group=letters[1:20])
head(data)</code></pre>
<pre><code>## ID group
## 1 1 a
## 2 2 b
## 3 3 c
## 4 4 d
## 5 5 e
## 6 6 f</code></pre>
<p>Combine the coordinates with the data</p>
<pre class="r"><code>spdf = SpatialPointsDataFrame(coords, data)
spdf = SpatialPointsDataFrame(sp, data)
str(spdf)</code></pre>
<pre><code>## Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
## ..@ data :'data.frame': 100 obs. of 2 variables:
## .. ..$ ID : int [1:100] 1 2 3 4 5 6 7 8 9 10 ...
## .. ..$ group: Factor w/ 20 levels "a","b","c","d",..: 1 2 3 4 5 6 7 8 9 10 ...
## ..@ coords.nrs : num(0)
## ..@ coords : num [1:100, 1:2] -0.7755 1.5926 1.038 -0.0797 -1.6608 ...
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : NULL
## .. .. ..$ : chr [1:2] "x" "y"
## ..@ bbox : num [1:2, 1:2] -2.82 -3.2 2.13 2.9
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : chr [1:2] "x" "y"
## .. .. ..$ : chr [1:2] "min" "max"
## ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
## .. .. ..@ projargs: chr NA</code></pre>
<p>Note the use of <em>slots</em> designated with a <code>@</code>. See <code>?slot</code> for more.</p>
</div>
<div id="promote-a-data-frame-with-coordinates" class="section level2">
<h2>Promote a data frame with <code>coordinates()</code></h2>
<pre class="r"><code>coordinates(data) = cbind(coords$x, coords$y) </code></pre>
<pre class="r"><code>str(spdf)</code></pre>
<pre><code>## Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
## ..@ data :'data.frame': 100 obs. of 2 variables:
## .. ..$ ID : int [1:100] 1 2 3 4 5 6 7 8 9 10 ...
## .. ..$ group: Factor w/ 20 levels "a","b","c","d",..: 1 2 3 4 5 6 7 8 9 10 ...
## ..@ coords.nrs : num(0)
## ..@ coords : num [1:100, 1:2] -0.7755 1.5926 1.038 -0.0797 -1.6608 ...
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : NULL
## .. .. ..$ : chr [1:2] "x" "y"
## ..@ bbox : num [1:2, 1:2] -2.82 -3.2 2.13 2.9
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : chr [1:2] "x" "y"
## .. .. ..$ : chr [1:2] "min" "max"
## ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
## .. .. ..@ projargs: chr NA</code></pre>
</div>
<div id="subset-data" class="section level2">
<h2>Subset data</h2>
<pre class="r"><code>subset(spdf, group=="a")</code></pre>
<pre><code>## class : SpatialPointsDataFrame
## features : 5
## extent : -0.775517, 1.043132, -2.460687, 0.8615845 (xmin, xmax, ymin, ymax)
## coord. ref. : NA
## variables : 2
## names : ID, group
## min values : 1, a
## max values : 81, a</code></pre>
<p>Or using <code>[]</code></p>
<pre class="r"><code>spdf[spdf$group=="a",]</code></pre>
<pre><code>## class : SpatialPointsDataFrame
## features : 5
## extent : -0.775517, 1.043132, -2.460687, 0.8615845 (xmin, xmax, ymin, ymax)
## coord. ref. : NA
## variables : 2
## names : ID, group
## min values : 1, a
## max values : 81, a</code></pre>
<p>Unfortunately, <code>dplyr</code> functions do not directly filter spatial objects.</p>
<div class="well">
<h2 id="your-turn">Your turn</h2>
<p>Convert the following <code>data.frame</code> into a SpatialPointsDataFrame using the <code>coordinates()</code> method and then plot the points with <code>plot()</code>.</p>
<pre class="r"><code>df=data.frame(
lat=c(12,15,17,12),
lon=c(-35,-35,-32,-32),
id=c(1,2,3,4))</code></pre>
<table>
<thead>
<tr class="header">
<th align="right">lat</th>
<th align="right">lon</th>
<th align="right">id</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="right">12</td>
<td align="right">-35</td>
<td align="right">1</td>
</tr>
<tr class="even">
<td align="right">15</td>
<td align="right">-35</td>
<td align="right">2</td>
</tr>
<tr class="odd">
<td align="right">17</td>
<td align="right">-32</td>
<td align="right">3</td>
</tr>
<tr class="even">
<td align="right">12</td>
<td align="right">-32</td>
<td align="right">4</td>
</tr>
</tbody>
</table>
<button data-toggle="collapse" class="btn btn-primary btn-sm round" data-target="#demo1">
Show Solution
</button>
<div id="demo1" class="collapse">
<pre class="r"><code>coordinates(df)=c("lon","lat")
plot(df)</code></pre>
<p><img src="04_Spatial_files/figure-html/unnamed-chunk-14-1.png" /><!-- --></p>
</div>
</div>
</div>
<div id="examine-topsoil-quality-in-the-meuse-river-data-set" class="section level2">
<h2>Examine topsoil quality in the Meuse river data set</h2>
<pre class="r"><code>## Load the data
data(meuse)
str(meuse)</code></pre>
<pre><code>## 'data.frame': 155 obs. of 14 variables:
## $ x : num 181072 181025 181165 181298 181307 ...
## $ y : num 333611 333558 333537 333484 333330 ...
## $ cadmium: num 11.7 8.6 6.5 2.6 2.8 3 3.2 2.8 2.4 1.6 ...
## $ copper : num 85 81 68 81 48 61 31 29 37 24 ...
## $ lead : num 299 277 199 116 117 137 132 150 133 80 ...
## $ zinc : num 1022 1141 640 257 269 ...
## $ elev : num 7.91 6.98 7.8 7.66 7.48 ...
## $ dist : num 0.00136 0.01222 0.10303 0.19009 0.27709 ...
## $ om : num 13.6 14 13 8 8.7 7.8 9.2 9.5 10.6 6.3 ...
## $ ffreq : Factor w/ 3 levels "1","2","3": 1 1 1 1 1 1 1 1 1 1 ...
## $ soil : Factor w/ 3 levels "1","2","3": 1 1 1 2 2 2 2 1 1 2 ...
## $ lime : Factor w/ 2 levels "0","1": 2 2 2 1 1 1 1 1 1 1 ...
## $ landuse: Factor w/ 15 levels "Aa","Ab","Ag",..: 4 4 4 11 4 11 4 2 2 15 ...
## $ dist.m : num 50 30 150 270 380 470 240 120 240 420 ...</code></pre>
<div class="well">
<h2 id="your-turn-1">Your turn</h2>
<p><em>Promote</em> the <code>meuse</code> object to a spatial points data.frame with <code>coordinates()</code>.</p>
<button data-toggle="collapse" class="btn btn-primary btn-sm round" data-target="#demo2">
Show Solution
</button>
<div id="demo2" class="collapse">
<pre class="r"><code>coordinates(meuse) <- ~x+y
# OR coordinates(meuse)=cbind(meuse$x,meuse$y)
# OR coordinates(meuse))=c("x","y")
str(meuse)</code></pre>
<pre><code>## Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
## ..@ data :'data.frame': 155 obs. of 12 variables:
## .. ..$ cadmium: num [1:155] 11.7 8.6 6.5 2.6 2.8 3 3.2 2.8 2.4 1.6 ...
## .. ..$ copper : num [1:155] 85 81 68 81 48 61 31 29 37 24 ...
## .. ..$ lead : num [1:155] 299 277 199 116 117 137 132 150 133 80 ...
## .. ..$ zinc : num [1:155] 1022 1141 640 257 269 ...
## .. ..$ elev : num [1:155] 7.91 6.98 7.8 7.66 7.48 ...
## .. ..$ dist : num [1:155] 0.00136 0.01222 0.10303 0.19009 0.27709 ...
## .. ..$ om : num [1:155] 13.6 14 13 8 8.7 7.8 9.2 9.5 10.6 6.3 ...
## .. ..$ ffreq : Factor w/ 3 levels "1","2","3": 1 1 1 1 1 1 1 1 1 1 ...
## .. ..$ soil : Factor w/ 3 levels "1","2","3": 1 1 1 2 2 2 2 1 1 2 ...
## .. ..$ lime : Factor w/ 2 levels "0","1": 2 2 2 1 1 1 1 1 1 1 ...
## .. ..$ landuse: Factor w/ 15 levels "Aa","Ab","Ag",..: 4 4 4 11 4 11 4 2 2 15 ...
## .. ..$ dist.m : num [1:155] 50 30 150 270 380 470 240 120 240 420 ...
## ..@ coords.nrs : int [1:2] 1 2
## ..@ coords : num [1:155, 1:2] 181072 181025 181165 181298 181307 ...
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : chr [1:155] "1" "2" "3" "4" ...
## .. .. ..$ : chr [1:2] "x" "y"
## ..@ bbox : num [1:2, 1:2] 178605 329714 181390 333611
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : chr [1:2] "x" "y"
## .. .. ..$ : chr [1:2] "min" "max"
## ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
## .. .. ..@ projargs: chr NA</code></pre>
</div>
</div>
<p>Plot it with ggplot:</p>
<pre class="r"><code> ggplot(as.data.frame(meuse),aes(x=x,y=y))+
geom_point(col="red")+
coord_equal()</code></pre>
<p><img src="04_Spatial_files/figure-html/unnamed-chunk-17-1.png" /><!-- --></p>
<p>Note that <code>ggplot</code> works only with data.frames. Convert with <code>as.data.frame()</code> or <code>fortify()</code>.</p>
</div>
</div>
<div id="lines" class="section level1">
<h1>Lines</h1>
<div id="a-line-is-a-single-chain-of-points." class="section level3">
<h3>A <code>Line</code> is a single chain of points.</h3>
<pre class="r"><code>L1 = Line(cbind(rnorm(5),rnorm(5)))
L2 = Line(cbind(rnorm(5),rnorm(5)))
L3 = Line(cbind(rnorm(5),rnorm(5)))
L1</code></pre>
<pre><code>## An object of class "Line"
## Slot "coords":
## [,1] [,2]
## [1,] -0.2266602 1.2389508
## [2,] 0.3506688 -0.6418654
## [3,] 0.5572550 -1.0022352
## [4,] -0.0470298 -1.2565673
## [5,] 0.4880012 0.3211727</code></pre>
<pre class="r"><code>plot(coordinates(L1),type="l")</code></pre>
<p><img src="04_Spatial_files/figure-html/unnamed-chunk-19-1.png" /><!-- --></p>
</div>
<div id="a-lines-object-is-a-list-of-chains-with-an-id" class="section level3">
<h3>A <code>Lines</code> object is a list of chains with an ID</h3>
<pre class="r"><code>Ls1 = Lines(list(L1),ID="a")
Ls2 = Lines(list(L2,L3),ID="b")
Ls2</code></pre>
<pre><code>## An object of class "Lines"
## Slot "Lines":
## [[1]]
## An object of class "Line"
## Slot "coords":
## [,1] [,2]
## [1,] -0.26960460 -1.4876681
## [2,] 0.06619791 -2.3025701
## [3,] 0.95283311 0.4591616
## [4,] -2.44938917 0.2783118
## [5,] -0.81758158 -0.4290159
##
##
## [[2]]
## An object of class "Line"
## Slot "coords":
## [,1] [,2]
## [1,] -0.3868302 -2.2222688
## [2,] -1.4941343 1.1255854
## [3,] -1.2185243 1.2088079
## [4,] 1.1479574 -0.3165272
## [5,] -1.6971661 0.1853546
##
##
##
## Slot "ID":
## [1] "b"</code></pre>
</div>
<div id="a-spatiallines-is-a-list-of-lines" class="section level3">
<h3>A <code>SpatialLines</code> is a list of Lines</h3>
<pre class="r"><code>SL12 = SpatialLines(list(Ls1,Ls2))
plot(SL12)</code></pre>
<p><img src="04_Spatial_files/figure-html/unnamed-chunk-21-1.png" /><!-- --></p>
</div>
<div id="a-spatiallinesdataframe-is-a-spatiallines-with-a-matching-dataframe" class="section level3">
<h3>A <code>SpatialLinesDataFrame</code> is a <code>SpatialLines</code> with a matching <code>DataFrame</code></h3>
<pre class="r"><code>SLDF = SpatialLinesDataFrame(
SL12,
data.frame(
Z=c("road","river"),
row.names=c("a","b")
))
str(SLDF)</code></pre>
<pre><code>## Formal class 'SpatialLinesDataFrame' [package "sp"] with 4 slots
## ..@ data :'data.frame': 2 obs. of 1 variable:
## .. ..$ Z: Factor w/ 2 levels "river","road": 2 1
## ..@ lines :List of 2
## .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
## .. .. .. ..@ Lines:List of 1
## .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
## .. .. .. .. .. .. ..@ coords: num [1:5, 1:2] -0.227 0.351 0.557 -0.047 0.488 ...
## .. .. .. ..@ ID : chr "a"
## .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
## .. .. .. ..@ Lines:List of 2
## .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
## .. .. .. .. .. .. ..@ coords: num [1:5, 1:2] -0.2696 0.0662 0.9528 -2.4494 -0.8176 ...
## .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
## .. .. .. .. .. .. ..@ coords: num [1:5, 1:2] -0.387 -1.494 -1.219 1.148 -1.697 ...
## .. .. .. ..@ ID : chr "b"
## ..@ bbox : num [1:2, 1:2] -2.45 -2.3 1.15 1.24
## .. ..- attr(*, "dimnames")=List of 2
## .. .. ..$ : chr [1:2] "x" "y"
## .. .. ..$ : chr [1:2] "min" "max"
## ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
## .. .. ..@ projargs: chr NA</code></pre>
</div>
</div>
<div id="polygons" class="section level1">
<h1>Polygons</h1>
<div id="getting-complicated" class="section level2">
<h2>Getting complicated</h2>
<p><img src="04_assets/polygons.png" alt="alt text" width="75%"></p>
<div id="issues" class="section level3">
<h3>Issues</h3>
<ul>
<li>Multipart Polygons</li>
<li>Holes</li>
</ul>
<p>Rarely construct <em>by hand</em>…</p>
</div>
</div>
</div>
<div id="importing-data" class="section level1">
<h1>Importing data</h1>
<p>But, you rarely construct data <em>from scratch</em> like we did above. Usually you will import datasets created elsewhere.</p>
<div id="geospatial-data-abstraction-library-gdal" class="section level2">
<h2>Geospatial Data Abstraction Library (<a href="gdal.org">GDAL</a>)</h2>
<p><code>rgdal</code> package for importing/exporting/manipulating spatial data:</p>
<ul>
<li><code>readOGR()</code> and <code>writeOGR()</code>: Vector data</li>
<li><code>readGDAL()</code> and <code>writeGDAL()</code>: Raster data</li>
</ul>
<p>Also the <code>gdalUtils</code> package for reprojecting, transforming, reclassifying, etc.</p>
<p>List the file formats that your installation of rgdal can read/write with <code>ogrDrivers()</code>:</p>
<table>
<thead>
<tr class="header">
<th align="left">name</th>
<th align="left">write</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left">AeronavFAA</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">ARCGEN</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">AVCBin</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">AVCE00</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">BNA</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">CartoDB</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">CouchDB</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">CSV</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">DGN</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">DXF</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">EDIGEO</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">ElasticSearch</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">ESRI Shapefile</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">Geoconcept</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">GeoJSON</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">GeoRSS</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">GFT</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">GME</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">GML</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">GMT</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">GPKG</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">GPSBabel</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">GPSTrackMaker</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">GPX</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">HTF</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">Idrisi</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">KML</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">MapInfo File</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">Memory</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">ODS</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">OpenAir</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">OpenFileGDB</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">OSM</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">PCIDSK</td>
<td align="left">TRUE</td>
</tr>
<tr class="odd">
<td align="left">PDF</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">PDS</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">PGDump</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">REC</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">S57</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">SDTS</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">SEGUKOOA</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">SEGY</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">SQLite</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">SUA</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">SVG</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">SXF</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">TIGER</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">UK .NTF</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">VFK</td>
<td align="left">FALSE</td>
</tr>
<tr class="even">
<td align="left">VRT</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">WAsP</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">WFS</td>
<td align="left">FALSE</td>
</tr>
<tr class="odd">
<td align="left">XLSX</td>
<td align="left">TRUE</td>
</tr>
<tr class="even">
<td align="left">XPlane</td>
<td align="left">FALSE</td>
</tr>
</tbody>
</table>
<p>Now as an example, let’s read in a shapefile that’s included in the <code>maptools</code> package. You can try</p>
<pre class="r"><code>## get the file path to the files
file=system.file("shapes/sids.shp", package="maptools")
## get information before importing the data
ogrInfo(dsn=file, layer="sids")</code></pre>
<pre><code>## Source: "/Library/Frameworks/R.framework/Versions/3.3/Resources/library/maptools/shapes/sids.shp", layer: "sids"
## Driver: ESRI Shapefile; number of rows: 100
## Feature type: wkbPolygon with 2 dimensions
## Extent: (-84.32385 33.88199) - (-75.45698 36.58965)
## LDID: 87
## Number of fields: 14
## name type length typeName
## 1 AREA 2 12 Real
## 2 PERIMETER 2 12 Real
## 3 CNTY_ 2 11 Real
## 4 CNTY_ID 2 11 Real
## 5 NAME 4 32 String
## 6 FIPS 4 5 String
## 7 FIPSNO 2 16 Real
## 8 CRESS_ID 0 3 Integer
## 9 BIR74 2 12 Real
## 10 SID74 2 9 Real
## 11 NWBIR74 2 11 Real
## 12 BIR79 2 12 Real
## 13 SID79 2 9 Real
## 14 NWBIR79 2 12 Real</code></pre>
<pre class="r"><code>## Import the data
sids <- readOGR(dsn=file, layer="sids")</code></pre>
<pre><code>## OGR data source with driver: ESRI Shapefile
## Source: "/Library/Frameworks/R.framework/Versions/3.3/Resources/library/maptools/shapes/sids.shp", layer: "sids"
## with 100 features
## It has 14 fields</code></pre>
<pre class="r"><code>summary(sids)</code></pre>
<pre><code>## Object of class SpatialPolygonsDataFrame
## Coordinates:
## min max
## x -84.32385 -75.45698
## y 33.88199 36.58965
## Is projected: NA
## proj4string : [NA]
## Data attributes:
## AREA PERIMETER CNTY_ CNTY_ID
## Min. :0.0420 Min. :0.999 Min. :1825 Min. :1825
## 1st Qu.:0.0910 1st Qu.:1.324 1st Qu.:1902 1st Qu.:1902
## Median :0.1205 Median :1.609 Median :1982 Median :1982
## Mean :0.1263 Mean :1.673 Mean :1986 Mean :1986
## 3rd Qu.:0.1542 3rd Qu.:1.859 3rd Qu.:2067 3rd Qu.:2067
## Max. :0.2410 Max. :3.640 Max. :2241 Max. :2241
##
## NAME FIPS FIPSNO CRESS_ID
## Alamance : 1 37001 : 1 Min. :37001 Min. : 1.00
## Alexander: 1 37003 : 1 1st Qu.:37050 1st Qu.: 25.75
## Alleghany: 1 37005 : 1 Median :37100 Median : 50.50
## Anson : 1 37007 : 1 Mean :37100 Mean : 50.50
## Ashe : 1 37009 : 1 3rd Qu.:37150 3rd Qu.: 75.25
## Avery : 1 37011 : 1 Max. :37199 Max. :100.00
## (Other) :94 (Other):94
## BIR74 SID74 NWBIR74 BIR79
## Min. : 248 Min. : 0.00 Min. : 1.0 Min. : 319
## 1st Qu.: 1077 1st Qu.: 2.00 1st Qu.: 190.0 1st Qu.: 1336
## Median : 2180 Median : 4.00 Median : 697.5 Median : 2636
## Mean : 3300 Mean : 6.67 Mean :1050.8 Mean : 4224
## 3rd Qu.: 3936 3rd Qu.: 8.25 3rd Qu.:1168.5 3rd Qu.: 4889
## Max. :21588 Max. :44.00 Max. :8027.0 Max. :30757
##
## SID79 NWBIR79
## Min. : 0.00 Min. : 3.0
## 1st Qu.: 2.00 1st Qu.: 250.5
## Median : 5.00 Median : 874.5
## Mean : 8.36 Mean : 1352.8
## 3rd Qu.:10.25 3rd Qu.: 1406.8
## Max. :57.00 Max. :11631.0
## </code></pre>
<pre class="r"><code>plot(sids)</code></pre>
<p><img src="04_Spatial_files/figure-html/unnamed-chunk-24-1.png" /><!-- --></p>
<div id="maptools-package" class="section level3">
<h3>Maptools package</h3>
<p>The <code>maptools</code> package has an alternative function for importing shapefiles that can be a little easier to use (but has fewer options).</p>
<ul>
<li><code>readShapeSpatial</code></li>
</ul>
<pre class="r"><code>sids <- readShapeSpatial(file)</code></pre>
</div>
<div id="raster-data" class="section level3">
<h3>Raster data</h3>
<p>We’ll deal with raster data in the next section.</p>
</div>
</div>
</div>
<div id="coordinate-systems" class="section level1">
<h1>Coordinate Systems</h1>
<ul>
<li>Earth isn’t flat</li>
<li>But small parts of it are close enough</li>
<li>Many coordinate systems exist</li>
<li>Anything <code>Spatial*</code> (or <code>raster*</code>) can have one</li>
</ul>
<div id="specifying-the-coordinate-system" class="section level2">
<h2>Specifying the coordinate system</h2>
<div id="the-proj.4-library" class="section level3">
<h3>The <a href="https://trac.osgeo.org/proj/">Proj.4</a> library</h3>
<p>Library for performing conversions between cartographic projections.</p>
<p>See <a href="http://spatialreference.org" class="uri">http://spatialreference.org</a> for information on specifying projections. For example,</p>
<div id="specifying-coordinate-systems" class="section level4">
<h4>Specifying coordinate systems</h4>
<p><strong>WGS 84</strong>:</p>
<ul>
<li>proj4: <br><small><code>+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs</code></small></li>
<li>.prj / ESRI WKT: <small><code>GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",</code><br><code>SPHEROID["WGS_1984",6378137,298.257223563]],</code><br><code>PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]</code></small></li>
<li>EPSG:<code>4326</code></li>
</ul>
<p>Note that it has no projection information assigned (since it came from a simple data frame). From the help file (<code>?meuse</code>) we can see that the projection is EPSG:28992.</p>
<pre class="r"><code>proj4string(sids) <- CRS("+proj=longlat +ellps=clrk66")
proj4string(sids)</code></pre>
<pre><code>## [1] "+proj=longlat +ellps=clrk66"</code></pre>
</div>
</div>
</div>
<div id="spatial-transform" class="section level2">
<h2>Spatial Transform</h2>
<p>Assigning a CRS doesn’t change the projection of the data, it just indicates which projection the data are currently in.<br />
So assigning the wrong CRS really messes things up.</p>
<p>Transform (<em>warp</em>) projection from one to another with <code>spTransform</code></p>