OpenSourcer (6) [Avatar] Offline
#1
Hi there

Chapter one is great for a newbie like me. Thanks. I had a problem with page 19 "linestrings and polygons."You mention that this creates a checkmark. As a newbie reading this, I am kinda lost. Its not clearly explained as to whether the check mark should be viewed in QGIS, etc. Should we see it in the database as myCheckMark, HeartLine, etc. Or is this supposed to be obvious and I'm just a lil dense smilie
regina.leo (265) [Avatar] Offline
#2
Re: Chapter 1
No not dense. You should be able to use QGIS or other tools to see it. We generally use OpenJump for adhoc queries. I think it will be a little clearer when we go over desktop tools for viewing.

Leo
OpenSourcer (6) [Avatar] Offline
#3
Re: Chapter 1
Ok. Thank you. smilie I just purchased the early access edition today. Just starting chapter 2. Will be asking loads of questions soon.
Christine_Bush (12) [Avatar] Offline
#4
Re: Chapter 1
"The popular mapping sites such as Google Maps, Virtual Earth, MapQuest, and Yahoo have empowered people in all walks of life to answer the question of “Where something is?” by finding it on a gorgeously detailed, interactive map. No longer were they restricted to textual descriptions of “where” like “Turn right at the supermarket and third house on right.” nor were they faced with the perennial problem of pulling out a paper map and not being able to figure out where they currently are."

1. "Where something is?" is not a question. "Where is something?" is a question.

2. "...empowered all walks of life" is cliche.

3. The statement that web maps have empowered all walks of life to find things is not true. There are still many people who are computer illiterate or who find web maps confusing and daunting, or who do not read English well enough to use them.

4. A web mapping application provides no more insight into where I am than a paper map does and requires an internet connection to use. They are littered with paid waypoints, street views and complicated options that do as much to obscure as to reveal anything about where I am. In fact, they are quite good as distracting me from where I am.

Nor is using a paper map a "perennial problem". If you want to make this argument, it should applied to the topic of the popularity of GPS devices which can show me where I am and are generally easier to use than paper maps.

5. Actually, this whole first paragraph is pretty weak. I'd just strike the whole thing and start the book with "Organizations large and small have learned that mapping is a great resource for analyzing patterns in data." This is unambiguous, clear and relevant to the topic of spatial databases.
Christine_Bush (12) [Avatar] Offline
#5
Re: Chapter 1
Page 2

"Spatial database comes to the rescue."

This stand alone statement seems to speak of the class of spatial databases coming to the resuce regarding a universal mapping problem. If so, then it should read:

"Spatial databases come to the rescue."
Christine_Bush (12) [Avatar] Offline
#6
Re: Chapter 1
Page 3

Again: header reads "What Is A Spatial Database" but is missing a question mark. The next paragraph is definitive, so obviously this should be "What Is A Spatial Database?"

Give it a try: type SHIFT + /

smilie
Christine_Bush (12) [Avatar] Offline
#7
Re: Chapter 1
Page 3

Should not the header that reads "What Is A Spatial Database" be un-indented so that it aligns with the left justification of Table 1.1 on this same page?
regina.leo (265) [Avatar] Offline
#8
Re: Chapter 1
Christine,

Thank you for your comments. That chapter does need a bit of work especially since its the first we wrote.

We are in the middle of revising the contents of the other chapters and finishing off the first draft of the last chapter.

We'll incorporate some of your suggestions when we revisit this chapter.

Thanks,
Leo and Regina
hglaser (3) [Avatar] Offline
#9
Re: Chapter 1
Hello-

On pg 12
"Back in the hay day of relational databases, object-relational was an interesting distinction,"

hay day should be revised to heyday


hey·day (hā'dā')
n. The period of greatest popularity, success, or power; prime.

[Perhaps alteration of heyda, exclamation of pleasure, probably alteration of Middle English hey, hey.]

The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
Cite This Source
regina.leo (265) [Avatar] Offline
#10
Re: Chapter 1
Holly,
Thanks for the catch. Will correct in next release.
Thanks,
Regina
Christine_Bush (12) [Avatar] Offline
#11
Chapter 1 (p16) and a request for style of URL references in general
On page 16, the URL for the Zero Milestone on Wikipedia is correct, but I suggest creating a project-wide style for listing URLs such that they are not included at the end of sentences where they are require to be followed by a period, such as happens here. The reason for this suggestion is simple: if you copy/paste the period from electronic text, the period sometimes breaks the URL. This is the case with Wikipedia.

Instead do something like this:

"...When the United States was a young (and small) nation, the city planners of the day intended for all roads to use this point to measure their distance. You can read more about it here:

http://en.wikipedia.org/wiki/Zero_Milestone"

Such conveniences, I suspect, are part of the secret of success for the DUMMIES franchise.

Message was edited by:
Christine_Bush
Christine_Bush (12) [Avatar] Offline
#12
Chapter 1 (p17) typo
This is the first sentence under LineStrings and Polygons:

"Now let us move onto more complex examples of creating linestrings and polygons."

It should instead read:

"Now let us move on ^ to more complex examples of creating linestrings and polygons."

Onto is a preposition, as in "She set her tea cup carefully onto its saucer."

On to is a phrasal verb, as in "The speaker moved on to the next topic" which is what you are doing here.

Message was edited by:
Christine_Bush
Christine_Bush (12) [Avatar] Offline
#13
Chapter 1 (p17) LineStrings and Polygons
"PostGIS is primarily used to store and query geographic data, but you have seen in the points examples that it can be used to represent any data that can be drawn on a Cartesian coordinate system."

Have we? I only saw from these examples that we can create points. The goal, and title, of this section seems to be to demonstrate that you can also represent other geometry types. This sentence might better read:

"PostGIS is primarily used to store and query geographic data. You saw in the previous examples how to represent point data. But we can also use PostGIS to represent any data that can be drawn using a Cartesian coordinate system."

Message was edited by:
Christine_Bush
Christine_Bush (12) [Avatar] Offline
#14
Re: Chapter 1 (p17) LineStrings and Polygons
"Common things we do are to convert plain text representations of locations such as longitude/latitude into a spatial data type of geometry or geography."

"Common things" is a plural phrase. "To convert plain text representations of locations" is a singular activity. Therefore, probably better:

"A common task is to convert plain text representations of a location, such as a pairs of longitude/latitude coordinates, into spatial data types such as geometry or geography."
regina.leo (265) [Avatar] Offline
#15
Re: Chapter 1 (p17) LineStrings and Polygons
Christine,

Thanks. That does sound much better. We'll update.

Leo
Christine_Bush (12) [Avatar] Offline
#16
Chapter 1 (p17) PostGIS Geography vs. Geometry measurement
In general, I notice that you do not offset the word "however" with a comma. This occurs twice in this section:

"However all measurements in geography are expressed in meters."

"However the measurements are always in the units of the spatial reference system."

I believe each of these sentences are more readable with a comma after the first word.

-----------------------------------------------------

Same paragraph, a different point:

"Data in the geography data type must always be stored in WGS 84 long lat degrees. However all measurements in geography are expressed in meters. If your source data is in a planar coordinate such as a State Plane ft or meters, you must load it as geometry, transform it and then cast it to geography if you want to use the geography data type storage."

This is a confusing subject that requires more clarity to convey here. i) Many readers may not appreciate that there are different lengths of foot. ii) I don't think there are different standards for meters, so it should be clarified what is happening in the conversion from State Plane meters to planar coordinate meters...perhaps even choose a different example altogether.

Break it apart, perhaps even with a graphic of some kind that demonstrates there are three different variables at play: data type, coordinate system, unit of measure.

1. Geometry is a data type that expresses a point, linestring or polygon as a two dimensional entity on a flat surface.

2. Geography is a data type that expresses a point, linestring or polygon as a two dimensional entity on a curved surface.

3. The geography data type has two storage requirements. It must have a spatial reference of WGS 84 and it must be sexagesimal (long/lat degrees, base 60).

4. In order to import geometric data for storage as a geographic data type requires at least two steps. It must be loaded as geometry first, then transformed to geographic. In order for the transformation to work properly, you may also need to first convert geometry from its provided unit of measurement to meters.

5. In order to import geometric data for storage as geometric data to perform accurate measurements or analysis, you only need to convert the data if it is sexagesimal or not using the unit of measurement you desire.

The best explanation of all this I've read is in Alastair Aitchison's "Beginning Spatial with SQL Server 2008" (ISBN 978-1-4302-1829-6, Apress 2009). He does a good job of answer the WHY. Degrees are *required* because you are representing a three dimensional object and your points, lines and polygons are being referenced against the center of the Earth instead of a grid. I am thinking specifically of the illustration in his work on p.12, Figure 1-7.

-----------------------------------------------------

"...This means if your data is long lat, your measurements will be in degrees. This is not useful for most kinds of analysis, so for geometry data, people often transform their data to a measurement preserving spatial reference system that is valid for their area of interest. Some common ones are UTM zones meter, State Plane Feet or meters, and thousands more."

1. measurement-preserving with a hyphen for clarity would be helpful
2. "Some common ones" followed by "...and thousands more" is inconsistent as "some" and "thousands" are not usually equated. Instead:

"...This is not useful for most kinds of analysis because it is not accurate. People transform their geometric data to a different unit of measure, and/or coordinate system, based on its extent for improved accuracy. Common geographic coordinate systems in the US are UTM, NAD83 or State Plane. There are thousands of others for different parts of the world, most of which can be expressed in different units of measure.