Merge pull request #27 from cforgaci/2-vector-cf

Update episode on geospatial concepts

episodes/08-intro-to-geospatial-concepts.Rmd

@@ -2,41 +2,54 @@
 title: 'Introduction to Geospatial Concepts'
 teaching: 10
 exercises: 2
-bibliography: references.bib
-zotero: true
+author: 'Ana Petrović'
 ---
 
 ::: questions
--   How ...
+
+-   How do you describe the location of a geographic feature on the surface of the earth?
+-   How do you describe different types of projections? 
+-   How do you decide on what CRS to use?
+
 :::
 
 ::: objectives
--   Describe ...
+
+-   Identify the CRS and projection that is best fit for a specific analytical question.
+
 :::
 
 ## The shape of the Earth
 
-The shape of the Earth is approximately a sphere which is slightly wider than it is tall, and which is called **ellipsoid**. The true shape of the Earth is an irregular ellipsoid, the so-called **geoid** (@fig-earth).
+The shape of the Earth is approximately a sphere which is slightly wider than it is tall, and which is called **ellipsoid**. The true shape of the Earth is an irregular ellipsoid, the so-called **geoid**, as illustrated in the image below.
 
-![The shape of the Earth. Source: United Nations Statistics Division and International Cartographic Association (2012a)](https://unstats.un.org/unsd/geoinfo/ungegn/docs/_data_icacourses/_ImagesModules/_selfstudy/S06_images/S06_03_a00.jpg){#fig-earth}
+```{r fig.cap="The shape of the Earth. Source: United Nations Statistics Division and International Cartographic Association (2012a).", echo=FALSE}
+knitr::include_graphics("https://unstats.un.org/unsd/geoinfo/ungegn/docs/_data_icacourses/_ImagesModules/_selfstudy/S06_images/S06_03_a00.jpg")
+```
 
-The most common and basic representation of the position of points on the Earth is the combination of the **geographical latitude and longitude**.
+The most common and basic representation of the position of points on the Earth is the combination of the **geographical latitude and longitude**, as shown below.
 
-![Geographical latitude and longitude. Source: van der Marel (2014).](fig/latlon.png)
+```{r fig.cap="Geographical latitude and longitude. Source: van der Marel (2014).", echo=FALSE}
+knitr::include_graphics("fig/latlon.png")
+```
 
-**Meridians** are **vertical** circles with constant longitude, called **great circles**, which run from the North Pole to the South Pole. **Parallels** are **horizontal** circles with constant latitude, which are called **small circles**. Only the equator (the largest parallel) is also a great circle.
+**Meridians** are **vertical** circles with constant longitude, called **__great circles__**, which run from the North Pole to the South Pole. **Parallels** are **horizontal** circles with constant latitude, which are called **__small circles__**. Only the equator (the largest parallel) is also a great circle.
 
-The black lines in @fig-latlon show the equator and the prime meridian running through Greenwich, with latitude and longitude labels. The red dotted lines show the meridian and parallel running through Karachi, Pakistan (25°45’N, 67°01’E).
+The black lines in the figure above show the equator and the prime meridian running through Greenwich, with latitude and longitude labels. The red dotted lines show the meridian and parallel running through Karachi, Pakistan (25°45’N, 67°01’E).
 
 ## Map projection
 
-**Map projection** is a systematic transformation of the latitudes and longitudes of locations on the surface of an ellipsoid into locations on a plane. It is a transformation of the three-dimensional Earth’s surface into its two-dimensional representation on a sheet of paper or computer screen (see @fig-projection for a comparison with flattening of an orange peel).
+**Map projection** is a systematic transformation of the latitudes and longitudes of locations on the surface of an ellipsoid into locations on a plane. It is a transformation of the three-dimensional Earth’s surface into its two-dimensional representation on a sheet of paper or computer screen (see the image below for a comparison with flattening an orange peel).
 
-![Map projection represented as flattening an orange peel. Source: Data Carpentry (2023)](https://datacarpentry.org/organization-geospatial/fig/orange-peel-earth.jpg){#fig-projection}
+```{r fig.cap="Map projection represented as flattening an orange peel. Source: Data Carpentry (2023).", echo=FALSE}
+knitr::include_graphics("https://datacarpentry.org/organization-geospatial/fig/orange-peel-earth.jpg")
+```
 
 Many different map projections are in use for different purposes. Generally, they can be categorised into the following groups: cylindrical, conic, and azimuthal (see @fig-projections).
 
-![Cylindrical, conic, and azimuthal map projections. Source: Knippers (2009)](https://kartoweb.itc.nl/geometrics/Bitmaps/Intro%201.9a.gif){#fig-projections}
+```{r fig.cap="Cylindrical, conic, and azimuthal map projections. Source: Knippers (2009).", echo=FALSE}
+knitr::include_graphics("https://kartoweb.itc.nl/geometrics/Bitmaps/Intro%201.9a.gif")
+```
 
 Each map projection introduces a **distortion** in geometrical elements – **distance**, **angle**, and **area**. Depending on which of these geometrical elements are more relevant for a specific map, we can choose an appropriate map projection. **Conformal projections** are the best for preserving angles between any two curves; **equal area (equivalent) projections** preserve the area or scale; **equal distance (conventional) projections** are the best for preserving distances.
 
@@ -73,13 +86,74 @@ In this workshop, we use two CRS shown in @tbl-crs.
 
 : Main properties of WGS 84 and Amersfoort / RD New coordinate reference systems {#tbl-crs}
 
+The figure below shows the same city (Rotterdam) in these two CRS.
+
+```{r fig.cap="Rotterdam in two different CRS", echo=FALSE}
+knitr::include_graphics("fig/rotterdam-crs.png")
+```
+
+In addition to using different CRS, these two maps of Rotterdam also have different scales. 
+
+
 ## Map scale
 
 **Map scale** measures the ratio between distance on a map and the corresponding distance on the ground. For example, on a 1:100 000 scale map, 1cm on the map equals 1km (100 000 cm) on the ground. Map scale can be expressed in the following three ways:
 
--   Verbal: 1 centimetre represents 250 meters
--   Fraction: 1:25000
--   Graphic:
+|||
+|---|----------| 
+|Verbal: | 1 centimetre represents 250 meters |
+|Fraction: | 1:25000 |
+|Graphic: | ![](fig/scalebar.png){width=75%} |
+
+::: challenge
+
+# Challenge: CRS for calculating areas
+
+You want to investigate which European country has the largest urban area. Which CRS will you use?
+
+a.	EPSG:4326
+b.	EPSG:28992
+c.	EPSG:3035
+
+Hint: Go to https://epsg.io/ or https://epsg.org/search/by-name and check properties of the given CRS, such as datum, type of map projection, units of measure etc. 
+
+::: solution
+
+Correct answer: c. EPSG:3035
+
+:::
+
+:::
+
+
+::: challenge
+
+# Challenge: CRS for calculating shortest paths
+
+You want to calculate the shortest path between two buildings in Delft. Which CRS will you use?  
+
+a)	EPSG:4326
+b)	EPSG:28992
+c)	EPSG:3035  
+
+Hint: Go to https://epsg.io/ or https://epsg.org/search/by-name and check properties of the given CRS, such as datum, type of map projection, units of measure etc. 
+
+::: solution
+
+Correct answer: c. EPSG:28992
+
+:::
+
+:::
+
+## References
+
+- Knippers, R. (2009): Geometric aspects of mapping. International Institute for Geo-Information Science and Earth Observation (ITC), Enschede. https://kartoweb.itc.nl/geometrics/ (Accessed 22-01-2024)
+
+- United Nations Statistics Division and International Cartographic Association (2012): 3. Plane rectangular coordinate systems – A) The ellipsoid / geoid. https://unstats.un.org/unsd/geoinfo/ungegn/docs/_data_icacourses/_HtmlModules/_Selfstudy/S06/S06_03a.html (Accessed 22-01-2024)
+
+- Van der Marel, H. (2014). Reference systems for surveying and mapping. Lecture notes. Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands. https://gnss1.tudelft.nl/pub/vdmarel/reader/CTB3310_RefSystems_1-2a_print.pdf (Accessed 22-01-2024)
+
 
 ::: callout
 # Useful resources
@@ -96,8 +170,7 @@ In this workshop, we use two CRS shown in @tbl-crs.
 :::
 
 ::: keypoints
--   Use `.md` files for episodes when you want static content
--   Use `.Rmd` files for episodes when you need to generate output
--   Run `sandpaper::check_lesson()` to identify any issues with your lesson
--   Run `sandpaper::build_lesson()` to preview your lesson locally
+
+-   ...
+
 :::