Open-File Report 99-5

On-line version

Calculation of Coal Resources Using

ARC/INFO* and EarthVision*: Methodology for the 

National Coal Resource Assessment 

By Laura N. R. Roberts1 and Laura R. H. Biewick1

1

U.S. Geological Survey, Denver, CO

This report is preliminary and has not been edited or reviewed for conformity with U.S. Geological Survey 

standards. * Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey

1999

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY
1

Introduction

This report documents a comparison of two

methods of resource calculation that are being used in

the National Coal Resource Assessment project of the

U.S. Geological Survey (USGS). Tewalt (1998) discusses the history of using computer software packages such as GARNET (Graphic Analysis of

Resources using Numerical Evaluation Techniques),

GRASS (Geographic Resource Analysis Support System), and the vector-based geographic information

system (GIS) ARC/INFO (ESRI, 1998) to calculate

coal resources within the USGS. The study discussed

here, compares resource calculations using ARC/

INFO* (ESRI, 1998) and EarthVision (EV)*

(Dynamic Graphics, Inc. 1997) for the coal-bearing

John Henry Member of the Straight Cliffs Formation

of Late Cretaceous age in the Kaiparowits Plateau of

southern Utah. Coal resource estimates in the Kaiparowits Plateau using ARC/INFO are reported in Hettinger, and others, 1996.

The initial steps for the ARC/INFO and the

EarthVision methods are the same. The input data

used for the resource calculations is an ASCII-formatted file consisting of 203 points with x and y

fields for location and a z field for the total net coal

thickness in beds >1 ft thick in John Henry Member.

Location data (x, y) units in meters are in Universal

Transverse Mercator projection (zone 12). Coal

thickness data units are in feet. This data file is introduced into EV and gridded. Once satisfied with the

position of the coal isopach lines generated from the

gridding process, the isopach lines are saved in

ASCII format as a 'contour output file', which is one

of the EV plotting options. The program 'ismarc',

which we received from the Illinois Geological

Survey (personal communication 1995, Colin Treworgy), is then used to convert the EV contour output

file to a file that is in 'arc-generate' format.

The output file from 'ismarc' is processed in ARC/

INFO using an Arc Macro Language (AML) program

(convert-ism.aml), also provided by the Illinois Geological Survey (personal communication 1995, Colin

Treworgy). This program converts the 'ismarc' output

file into an ARC/INFO polygon coverage. Each polygon created using this AML is attributed with a value

for net coal thickness, which is an average of the

thickness values of the two contour lines on either

side of the polygon. For example, if the contour interval is 10 feet, then the entire area between the 20- and

30-ft. contours is attributed with the thickness value

of 25 ft. The ARC/INFO coverage for thickness is

unioned with the other polygon coverages representing geologic and other spatial information for which

tonnages are to be reported, (i.e., county, 7.5' quadrangle, township, surface and coal ownership, reliability, overburden thickness, etc.). Figure 1 shows

polygons within the unioned polygon coverage for a

part of the study area with labels for the thickness

value that was generated using the AML program. 

ARC/INFO

Thickness values generated using the 'convertism' AML (fig. 1) are used to calculate coal volume.

To calculate coal tonnage using ARC/INFO, two

items were added to the final unioned coverage:

'Acreft' - a numeric field calculated by multiplying the

area in square meters by .0002471 (the number of

square meters per acre) times the net coal thickness

(in feet) and 'Shtons_bit' - a numeric field calculated

by multiplying the field for 'Acreft' by 1800 (the number of short tons per acre-foot for bituminous-rank

coal; Wood and others, 1983).

Calculation of Coal Resources Using

ARC/INFO* and EarthVision*: Methodology for the

National Coal Resource Assessment 

By Laura N. R. Roberts1 and Laura R. H. Biewick1
2

EarthVision

To calculate coal tonnages using EV, the same

unioned polygon coverage that is used in the ARC/

INFO calculations is imported into EV as a single

polygon file. Although multiple attributes are associated with the individual polygons, the user is allowed

only one attribute to label when importing the

unioned polygon. We use the 'coverage-id' attribute to

label the individual polygons within the polygon file

because it is a unique identifier. 

The volumetrics utility within EV is used to calculate short-tons of coal. The thickness values of the

grid nodes from the 2-dimensional grid of coal thickness, supply the thickness values used to calculate the

coal tonnage within each polygon. This grid is the

same one used in the preceding process to generate

the polygon coverage of coal thickness. The volumetrics routine produces an ASCII-formatted volumetrics

report that lists by polygon-id (coverage-id) the area

and short tons for each polygon within the polygon

file. A program was written at the USGS called 'evrpt'

that converts this volumetrics report to a tab-delimited

ASCII-formatted file (personal communication 1997,

Dorsey Blake). 'Evrpt' also calculates the coal thickness value that EV uses to calculate short-tons for

each polygon and writes the value to a column. The

thickness values in this file will often be different than

those that are used to calculate coal tonnage using the

ARC/INFO method. Consequently, the total coal tonnage values may also differ. Figure 2 shows the same

part of the unioned polygon as that in figure 1. The

labels in this figure, however, represent the thickness

that the volumetrics routine in EV used to calculate

the short tons values. The shaded areas in figures 1

and 2 highlight those polygons where the thickness

values are significantly different.

Discussion

Tables 1 and 2 are a comparison of the John

Henry Member coal resources rounded to millions of

short tons as calculated by the two techniques.

Results are reported by County and by overburden

thickness (table 1). As can be seen in the table, the

tonnage values for the total area and for large areas

such as an entire County are very similar (differing

by < 1 percent). Table 2 shows tonnage reported by

Townships. The larger differences in tonnage values

are for small areas and for areas adjacent to lines of

a polygon that represent coal isopachs.

References Cited

Dynamic Graphics, Inc., 1997, EarthVision,. v. 4.

ESRI - Environmental Systems Research Institute, Inc., 1998, ARC/INFO, 

v.7.1.1.

Hettinger, R.D., Roberts, L.N.R., Biewick, L.R.H., and, Kirschbaum, M.A., 

1996, Preliminary investigations of the distribution and resources of 

coal in the Kaiparowits Plateau, southern Utah, U.S. Geological Survey Open-File Report 96-539, 72 p.

Tewalt, S.J., 1998, National coal resource assessment methodology: 

Comparison of resource calculation methods by two geographic 

information systems (GIS): U.S. Geological Survey Open-File Report 

98-365, 5 p.

Wood, G. H., Jr., Kehn, T.M., Carter, M.D., and Culbertson, W.C., 1983, 

Coal resource classification system of the U.S. Geological Survey: 

U.S. Geological Survey Circular 891, 65 p.
3

37.5 42.5 37.5 32.5 32.5

37.0 32.5 32.5

27.5

42.5

32.5

32.5

27.5

37.5

37.5

37.5

27.50

32.5 32.5 32.5 32.5

32.5 37.5 32.5

27.5 32.5

32.5

27.5

27.5

27.5

27.5

32.5 32.5

32.5

32.5

32.5

32.5

32.5 32.5

37.5

37.5

37.5

22.5

27.5

27.5 22.5

32.5

32.5

27.5

32.5

22.5

27.5

22.5

27.5 32.5

27.5

27.5

22.5

32.5

27.5

22.5

27.5

22.5

17.50

27.5 27.5

27.5

32.5

22.5

17.5

27.5

22.5

17.5

17.5

22.5 17.5

17.5

17.5 22.5

12.5

12.5

22.5

12.5

12.5

17.5

17.5

17.5 17.5

22.5

7.5

17.5

7.5

12.5

22.5

12.5 12.5

12.5

12.5

12.5

17.5

17.5

12.5

17.5

Figure 1. Net coal thickness values generated in ARC/INFO using ’convert-ism.aml’ for

an area in the Kaiparowits Plateau, Utah

15

15

10

30

35

20

25

1 mile (approximately)

Example of area with thickness 

difference between 8% and 25%

of same area in Figure 2

Scale

40

Outline of Township 35 South, 

Range 2 West, Short tons of 

coal recorded in table 2

15 Isopach line

Net coal thickness 

for polygon
4

42.0 42.3 31.3 37.4

33.3 37.9 31.2 33.7

28.8

40.4 34.1 34.4

27.4

38.3 39.2 29.4

34.1 30.9 31.8 32.7

34.6

33.7

33.0 39.7

29.9 33.1 35.0 26.2

26.0

27.0

27.5

30.2 30.5

30.9

31.3

31.2

33.0 33.1

32.6

33.1

35.5

36.0

36.6

24.8 28.2

27.4 22.7

32.2

27.7

31.9 32.6

21.4

28.6

22.6

29.9 30.4

29.3

27.7

22.5

30.3

29.4 24.9

29.9

22.2

19.9

25.8 27.1

27.3

30.1

22.0 17.5

27.5

17.3 22.8

17.7

23.8 19.8

18.0

22.1

15.9

11.8

11.6

23.2

14.1

14.1

19.4

 9.8

19.3

20.6

20.0

10.0

12.7

22.8

19.8

13.0

13.1

14.4

14.5

19.2

15.8

17.8

13.5

17.0

15

15

10

30

35

20

25

1 mile (approximately)

40

Scale

12.5

Figure 2. Net coal thickness values generated by the ’evrpt’ program from data 

in the EarthVision volumetrics report for an area in the Kaiparowits Plateau, Utah

Example of area with thickness 

difference between 8% and 25%

of same area in Figure 1

Outline of Township 35 South, 

Range 2 West, Short tons of 

coal recorded in table 2

15 Isopach line

Net coal thickness 

for polygon
5

Table 1. Comparison of coal resources (in millions of short tons) by County for the John Henry Member of the 

Straight Cliffs Formation, Kaiparowits Plateau, Utah using the two different resource calculation methods.

EarthVision (grid method)

Overburden (ft) 

County 0-1000 1000-2000 2000-3000 3000-6000 >6000 Grand Total

Garfield 2814 7004 4465 11696 1748 27727

Kane 13469 9354 10981 696 0 34501

Grand Total 16283 16358 15446 12392 1748 62228

ARC/INFO (average contour value method)

Overburden (ft) 

County 0-1000 1000-2000 2000-3000 3000-6000 >6000 Grand Total

Garfield 2841 6994 4464 11678 1735 27713

Kane 13532 9370 10999 696 0 34597

Grand Total 16373 16364 15464 12374 1735 62310

% Difference

County 0-1000 1000-2000 2000-3000 3000-6000 >6000 Grand Total

Garfield 1.0 0.1 0.0 0.2 0.7 0.1

Kane 0.5 0.2 0.2 0.0 0.0 0.3

Grand Total 0.5 0.0 0.1 0.1 0.7 0.1

EarthVision ARC/INFO

Township Grand Total Township Grand Total % Difference

33S1E 2016 33S1E 2016 0.0

33S1W 616 33S1W 615 0.2

33S2E 277 33S2E 277 0.0

33S2W 124 33S2W 124 0.0

34S1E 1712 34S1E 1711 0.1

34S1W 3523 34S1W 3527 0.1

34S2E 46 34S2E 46 0.0

34S2W 1723 34S2W 1724 0.1

35S1E 945 35S1E 939 0.6

35S1W 2163 35S1W 2150 0.6

35S2E 2 35S2E 2 0.0

* 35S2W 671 * 35S2W 676 0.7

36S1E 1865 36S1E 1841 1.3

36S1W 1431 36S1W 1433 0.1

36S2E 1414 36S2E 1415 0.1

36S2W 229 36S2W 232 1.3

36S3E 270 36S3E 271 0.4

37S1E 2920 37S1E 2922 0.1

37S1W 476 37S1W 487 2.3

37S2E 4195 37S2E 4186 0.2

37S3E 1084 37S3E 1091 0.6

37S4E 18 37S4E 21 14.3

38S1E 1314 38S1E 1314 0.0

38S1W 31 38S1W 32 3.1

38S2E 3850 38S2E 3849 0.0

38S3E 3561 38S3E 3562 0.0

38S4E 994 38S4E 993 0.1

38S5E 52 38S5E 57 8.8

Table 2. Comparison of coal resources (in millions of short tons) by Township for the John Henry Member of the Straight 

Cliffs Formation, Kaiparowits Plateau, Utah using the two different resource calculation methods. Township with asterisk 

is outlined in figures 1 and 2.
6

39S1E 870 39S1E 868 0.2

39S1W 5 39S1W 7 28.6

39S2E 3302 39S2E 3302 0.0

39S3E 4579 39S3E 4579 0.0

39S4E 2391 39S4E 2390 0.0

39S5E 2670 39S5E 2669 0.0

39S6E 18 39S6E 28 35.7

40S1E 136 40S1E 155 12.3

40S1W 2 40S1W 6 66.7

40S2E 1804 40S2E 1806 0.1

40S3E 3075 40S3E 3076 0.0

40S4E 245 40S4E 245 0.0

40S5E 885 40S5E 885 0.0

40S6E 105 40S6E 116 9.5

40S7E 1 40S7E 4 75.0

41S2E 541 41S2E 551 1.8

41S3E 1375 41S3E 1379 0.3

41S4E 1620 41S4E 1595 1.6

41S5E 571 41S5E 567 0.7

41S6E 2 41S6E 2 0.0

41S7E 16 41S7E 28 42.9

41S8E 1 41S8E 3 66.7

42S2E 82 42S2E 88 6.8

42S3E 318 42S3E 335 5.1

42S4E 71 42S4E 70 1.4

42S8E 4 42S8E 19 78.9

43S3E 19 43S3E 21 9.5

Grand Total 62228 Grand Total 62310 0.1

Table 2. Comparison of coal resources (in millions of short tons) by Township for the John Henry Member of the Straight 

Cliffs Formation, Kaiparowits Plateau, Utah using the two different resource calculation methods. Township with asterisk 

is outlined in figures 1 and 2—Continued.